During your workout you breakdown your muscles causing micro tears. The amino acids within protein help repair and maintain your muscles.
Every time we breakdown our muscles and provide our body with enough protein it will repair. Over time the muscle will increase in size and strength as a result of this process.
So you might be asking yourself how much protein do you need ?
Well the recommendation for building muscle is a gram of protein for every pound of bodyweight. For example if you weigh 180 pounds then you should aim to consume180 grams of protein.
Generally the best way to increase protein in your diet is through lean meats, nuts and supplements.
To get the best results from your training I would recommend tracking how much protein you are consuming in your diet.