The first supplement that a starter should begin taking is a whey protein supplement. Whey protein is an extremely fast absorbing protein and because of that is the best protein to take after a workout, when all your muscles are in need of protein to rebuild themselves. Whey can also be consumed early in the morning after your body has undergone around 8 hours of fasting. Whey should not be mixed with milk as milk slows down the absorption rate that whey protein is so famous for. Whey should be mixed with water and dextrose and maltodextrin postworkout.
After you have passed from your "beginner" stage to the "amateur" stage, you might want to start taking creatine. Creatine is found in our muscles and helps produce energy and strength. Creatine is found naturally in red meat, but supplementation with creatine causes the muscles to be saturated with creatine and causes huge strength and size gains. Creatine supplements are not dangerous when taken used according to the maker's instructions, but you should always speak to your physician prior to taking creatine. Starting creatine usually involves a "loading" phase, where a lot of creatine is taken in the first 5 days or so, and then the regular amount is taken following that. While on creatine, it is paramount to consume a large amount of water; upwards of a gallon a day is preferred, otherwise liver damage could occur.
Supplements are one of the most important parts of fitness and yet they are very often misunderstood by beginners. When supplements are taken correctly, there are little to no ill effects and many benefits to be had.