Yes, I did say worthless, that was not a long, 9 word typo. Building muscle could be like... Building a house. Now, building a house without bricks is going to leave it very unfinished. Nobody is going to buy the house, and you wouldn't want that, would you?
Same applies to muscles, building muscle without proper nutrition will leave the muscles carbohydrate resources depleted, and the fibers damaged. Depleted and damaged sounds plain awful, doesn't it? It actually is good, but just for short periods of time. Why? Muscle breaks down in order to repair itself into a stronger version, to accomplish the action you wanted to do.
Now that you know this, let's get into the fun part. Eating.
After your work outs, you simply need two things. Carbohydrates and protein.
Do you want some suggestions? Sure:
Now, what should you not eat? You should not eat anything that contains FAT. Fat slows down the digestion. Meaning it would slow down the digestion of the carbs and protein you just ate, which you don't really want. You're not sure why you don't want that, you might say "it's going to be digested sooner or later, anyways.". Well, there's this thing called 'the golden hour', it's the first hour after your work out.
During the first hour, your glycogen stores are depleted. So enzymes which convert glucose to glycogen are rushed to your muscles in order to quickly repair the stores. The post-workout meal is very important in order to replace the nutrients and fluids. You should also not forget to drink a lot of water.
However.. Any small amount of carbohydrates won't do. You must eat enough carbohydrates in order to trigger insulin. Insulin is the harmone which shoves carbs and amino acids into your muscles. In doing this, the carb resynthesis speeds up and protein start to rapidly repair the broken tissue of your muscles.
You should always consider and think about your post-workout meals, without properly eating after work-outs, you may be possibly working out for nothing.