However a manufacturer wishes to dress up a supplement - "sports supplements", "bodybuilding supplements", "diet supplements", "health supplements" - and the wonder claims associated with such supplements, you must first consider the fact that it's a supplement - something to add.
When considering the above in a food context, successful supplementation will be to fulfill your nutritional requirements. Genetic differences aside, a very basic nutritional example is anyone involved within sports. The individual's protein and overall calorific requirements will be greater than a sedentary individual of similar weight. Although they may find it easy to increase their carbohydrate and fat intake at meals, they're unlikely to consume an extra couple of chicken breasts a day. Subsequently, although their calorie intake may've increased slightly (through largely carbohydrates and fats), their percentage of protein intake is lower, not greater. Therefore, perhaps the most common form of supplementation is that of convenient protein shakes. Again though, this is to fulfill your nutritional requirements - to have as well as, not instead of.
Fulfilling your nutritional requirements with, or without, supplementation can make a huge difference to both your training and quality of life. In short, the most important supplements will be your key nutrients, but, in certain circumstances, and depending upon your training and related goals, other supplements can be of benefit. Across the Gym Professor website (whether already or in the near future), I (GP) have independently addressed many aspects of diet, training and supplementation to help answer your questions and help toward your goals.