When you lift weights you cause your muscles to strain.  The muscle fibers actually get tiny tears from the stress.  This triggers your body to repair and rebuild the damaged fibers through muscle protein synthesis.  One of the best supplements for your body during this process is a vanilla protein shake.  

As you may have guessed, protein is necessary for this process.  Protein provides the building blocks for muscle growth and repair.  These building blocks are call amino acids.  On a lifting day, you are actively breaking down muscle tissue.  Your body is using amino acids to repair and rebuild.  So, you need a steady supply of protein.  Depending on how strenuous your lift, your body can be doing muscle protein synthesis up to 24-48 hours after  your workout.

It is important to provide  your body with enough protein.  The best way to do that is by eating high-protein foods throughout the day.  Good sources of protein are lean meats, fish, eggs, diary, beans, nuts, and protein supplements.

The target amount of protein can very depending on your muscle mass and how hard your worked out, but the American College of Sports Medicine suggests you consume 1.2-1.7 grams of protein per kilogram of body weight per day.