Before anything else, remember that protein supplements are… supplements. You supplement them to your natural protein intake to help you reach certain amino requirements. They are not meant to be your exclusive protein source.
Proteins are broken down in the body into amino acids, the building blocks of muscle fibre. So, it could be said protein is muscle (put very simply). When you are eating a steak you are eating an animals muscle, so the main nutrient present is protein. It is shown that to build lean muscle a person needs atleast 1 gram of protein per 1lb of lean bodymass (overall weight minus bodyfat %) daily. This ofcourse is always up for debate, but is a good target to go by if you’e looking to build serious muscle tone. For some people this might be a target too hard to reach. In this case you can supplement your protein requirements with a protein shake.
There are 2 main types of protein (which can be mixed), Whey Protein and Casein Protein.
Whey protein is derived from Cows Milk, is fast acting and contains little to no fat or cholesterol. Being fast acting it is perfect for times when your body needs a quick surge of amino acids, like before/after training and in the morning.
Casein protein is also derived from milk, but is a found as suspended particles not soluble like whey. Being less soluble whey protein forms a sort of gel in your stomach, making it harder to digest. This equates to a slower release time, gradually providing amino acids to the body. This type of protein is perfect for when you expect not to eat for some time, like bedtime. While asleep, your body is constantly fed protein over a long duration, which is perfect for recovery at rest.
Be sure to go to Fitness/Nutrition stores for protein, not Health Food stores, as proteins made for bodybuilding are of a higher grade, and cheaper. I get mine from IrishLifting.com. Make sure you dont buy a weight gain (full of carbs), and that carb and fat levels are low (atleast under 2 grams each!!!).