L-Carnitine

Many athletes, and nearly all bodybuilders, supplement with some type of protein powder. Getting all of your macronutrients solely from food (your diet) isn't the easiest thing to do when you have and are building considerable muscle mass. Sometimes you go over your daily calorie limit trying to get enough protein, or maybe you end up taking in too much fat.
With a protein powder like whey or casein, you're able to get a huge boost of protein without doing those things. You also spend much less time eating, since a shake in a blender bottle takes very little time out of your day.
What Are Whey and Casein Protein?
Whey is considered to be a fast digesting protein. It's what people will recommend one takes directly before or after resistance training, as your body will metabolize it more quickly than casein.
Casein, on the other hand, is considered a slow digesting protein. Most proteins will be considered slow, especially when taken with a mixed meal as many people tend to do (think steak and potatoes with a side of veggies).
How Whey (Powder) is Made
It's essentially what's left over after milk has been curdled and strained when producing cheese. The milk curdles (casein), and the leftover liquid (whey) is then dried into a powder by separating the water from it.
How Casein (Powder) is Made
Like whey, casein comes from milk as well and it's the predominant protein in milk. Once the milk curdles, those curdles are then dehydrated into casein powder.
Casein and Whey Protein (Milk) Promote Lean Mass
In a study conducted on 56 healthy, untrained males over 12 weeks, skim milk was overall superior to that of soy milk and an isocaloric carbohydrate drink. Those drinking the milk saw the biggest decrease in body fat and the biggest increase in muscle mass (hypertrophy).
One thing that we can take away from this study is that a mixture of whey and casein are great for building mass and increasing strength. So the question still remains unanswered: which of the two is superior in that respect?
Whey Stimulates Protein Synthesis
Since whey protein is a much faster digesting protein compared to casein, it's able to more rapidly augment protein synthesis. One reason is due to its higher level of leucine — an amino acid that stimulates such synthesis.
The digestion rate of protein is an independent regulating factor of postprandial protein retention: https://www.ncbi.nlm.nih.gov/pubmed/11158939 The acute and abundant amounts of amino acids that enter your blood from whey is what's doing the heavy lifting when it comes to protein synthesis. With whey, you're able to metabolize the protein quickly, resulting in a spike of amino acids in your blood.
Casein Helps Prevent Muscle Breakdown
Because of casein's slower digestion rate, it can help to create a positive protein balance that prevents the catabolism of muscle by prolonging the duration that amino acids stay in your blood.
Slow and fast dietary proteins differently modulate postprandial protein accretion: https://www.ncbi.nlm.nih.gov/pubmed/9405716 Our Recommendation
Whey. Casein is much easier to come by in your regular diet; you can drink milk, and you can eat cheeses or meats.
If you're going to buy a supplement in powdered form, whey just seems like the most appropriate choice. Take it before or after a workout (or both), and you'll be be metabolizing that protein much quicker than if you bought the casein variation.
There's definitely efficacy to those that answer this with "use both," but purely in terms of a powdered form that you spend your hard-earned money on... whey is the way.
 
To summarize and avoid confusion: both of these are important and we certainly recommend getting both types of protein everyday. Casein you'll simply have through meals, and whey you can pick up as a supplement to take before and after your workout and first thing in the morning.

The difference can be confusing for the mere fact that you supplement your diet by taking vitamins, or you take supplements that contain vitamins. While the two like to intertwine, there is a small difference between what they are.
Vitamins
Vitamins technically fall under the supplement category. Like I mentioned above, you can supplement your diet with vitamins. These will generally come in pill-form, and sometimes in powdered form such as with some forms of vitamin C, like calcium ascorbate.
Some other examples of vitamins include:
Vitamin D Folic acid (vitamin B9) Vitamin B12 Vitamin A Many more... Another way of getting vitamins that many people don't realize is through fortified foods. Because many vitamins are hard to come by in food (vitamin D for example), there are many foods available that have been fortified with vitamins. Depending on the country and its food regulations, fortified foods may be more common in some areas of the world compared to others. 
Supplements
Supplements, on the other hand, are a wider variety of dietary products that may contain vitamins, minerals, herbs, and other nutrients. A good example of a supplement is creatine; it's produced in the body, but many people supplement with it due to the health and athletic benefits it provides. 
Some other examples of supplements include:
Fish Oil Ginseng Glutamine The list goes on — there are far too many supplements to list here.
Vitamins nor Supplements Are FDA-backed
Supplements are not regulated by the Food and Drug Administration, contrary to what many may believe. This is due to the fact that, for things to be approved by the FDA, they need to be scientifically scrutinized to their standards. This isn't to say that science hasn't shown the potential of certain supplements, but just that they haven't quite met the standards of the FDA.
When purchasing a supplement, it's important to know the quality of the product you're purchasing. Buy from reputable companies that do third-party testing, as the FDA isn't the one checking your supplements to see if they're legitimately healthy for you.
A great source that does their own testing on popular brands is Labdoor. This site tests and ranks supplements and they are free of manufacturer biases. They even give science reports on individual products along with infographs.

Concluding...
To recap, a vitamin is something you can supplement and it falls under the supplement category. Supplements, however, are a wider variety of substances that are aimed at bettering one's health and don't always need to have vitamins in them.
A vitamin can be in the form of a supplement, but a supplement need not be a vitamin.
Always be wary of who you're buying products from and try to find the most reputable sources for your supplements. If something seems cheaper than the rest of its competitors, this should raise a red flag and you may want to look elsewhere. You are, after all, supplementing for health reasons — so buy products you know are good for your body.

Creatine is a highly scrutinized supplement and among the most popular used with both amateur and professional athletes. It's a molecule that is naturally produced in the body and aids our bodies by releasing energy during intense physical activity and stress. This causes us to gain additional strength after supplementation.
Along with its cardio- and neuro-protective  properties, creatine has a variety of health benefits.
The most popular form, and the one recommended by most including Androgrow, is creatine monohydrate. Another popular form is creatine nitrate, which you may find touted as a superior version of creatine. This is untrue and you should be wary of these claims. There is no evidence to support that any other form of creatine is superior to its monohydrate version.
While creatine is a vitamin-like compound, it's not considered a vitamin due to the fact that we produce it within our bodies.
Another great benefit of creatine is that it increases dihydrotestosterone.
Amount of Creatine to Take
The common recommendation is to take 3-5 grams of creatine per day, everyday.
Creatine Loading
There is also no need to load creatine, as your muscles will become saturated over time while taking a maintenance dose. There is efficacy to the notion that you will get the benefits of creatine more quickly if you load it. As cheap as the supplement can be, it's not necessarily a waste to do so, nor should there be any harm in loading 15-25g per day for a week. A may accurate way of calculating your loading amount would be to take 0.3 grams per KG of body weight.
Cycling and Kidney Problems
Contrary to oldschool beliefs, there is no need to cycle creatine and it does not cause kidney problems. Even if taken in large amounts (20g and upward) by an individual with less-than-optimal kidney function, there is no damage. With that in mind, always consult your doctor if you are known to have kidney issues, or even if you're simply worried about supplementation of any kind.
Water Retention
Water retention from creatine is stored in skeletal muscle. There are people that will say creatine will make you bloat, which is not necessarily true. With proper intake, you should not have much, if any, subcutaneous water retention.