As many of you know, I'm not a huge proponent of taking supplements. I do however suggest that folks take a multiple vitamin, and antioxidant and omega-3. 
The word supplement refers to aomething added to complete a thing, make up for a deficiency, or extend or strengthen the whole. Therefore, a nutritional supplement is just that; adding something to make up for a difficiency. Knowing that most of us do not get enough vitamins and minerals from food alone, we must add them somehow. Those restrictig intake or with high outputs need
more because of caloric deficits.
In terms of performance, there are no magic pills that will make you run faster, jump higher or lose bodyfat.
There's no supplementing hard work!
There are a few substances outside of steroids and human growth hormone that have demonstrated that in the right environment, the can be used to help athletes.
1. Caffeine
2. Creatine monohydrate

there is endless reading material on both of these and I will direct you away from the bullshit marketing that has inundated the fitness community. Be warned, there is absolutely NO regulation of the supplement industry. The only way to determine of a product is worthy or your time, money and ingestion is to research it!

I was a clown working at GNC during college and learned the In's and Out's to a reasonable degree. As a result of a huge employee discount and no sence of what I was doing, I experimented with creatine when it first came on the market in the early 90's. Yes I'm that old. It worked. Now I must make you aware that the infamous placebo effect is significant, but if that's all it was, i still worked. 
Caffeine is a stimulant that also works to increase metabolism among other things.
The only company I will use for my vitamins and potential ergogenic aids is Apex Fitness. They have garbage products like all other companies. It is a business. However, their product is manufactured by a pharmaceutical company, Phoenix Labs. His process is the under the same scrutiny as medicine. Those of you subject to drug testing should take this seriously. There is evidence that shows significant contamination of supplements due to the lack of regulation. Most supplements are made in China and Germany.

I have no ties to Apex and make no money whatsoever promoing them. If I did, you'd see their logo on my website and I'd constantly be telling you to take their stuff.

Read, learn and make an informed decision!    
www.apxfitness.com