Supplements is a ridiculously complicated topic. I'd recommend reading "The Perfect Health Diet" by Paul Jaminet. It has a section on supplements and breaks down what you need and why, which foods they are found in, and which vitamins/minerals work hand in hand (for example, if you are low on magnesium, your vitamin D supplement won't be absorbed by your body). From there, you can figure out, based on your own diet, what you need to supplement.