Yes, you should absolutely add protein powder to your diet.
You want to make sure you use Whey Protein for after you workout. It is the fastest absorbing protein and is perfect for post workout recovery. After your workout, your body needs to rebuild the muscles you broke down. It will either get that protein from your protein shake, or it will get protein from your muscles (which essentially means you are robbing some of your muscles to feed others). Take the protein shake to avoid this.
I would take ~2 scoops (40-50g) of protein immediately after your workout (within 15 minutes). Mix it with water (or milk if you either want the extra calories, or the taste).
Any brand will work. The two I have used that I recommend are Optimum Nutrition Gold Standard or Dymatize Elite Whey Protein Isolate. I am currently using the first one because it also has Glutamine and BCAA's in it. I have used GNC Pro Performance 100% Whey Protein, but I don't recommend it as strongly because it has a lot of fillers.
As for amount of protein in a day, different people will tell you different things. A good middle ground is 1g of protein per lb of goal weight. So I am 180lbs and my goal is 195. I try to eat ~195g of protein a day.
The only other time I take a protein shake is when I can't eat a normal meal, but want protein in my body. For instance if I am about to go to the gym, and I haven't eaten in several hours, I will take a scoop or two before the gym. Or if I need to skip lunch (last resort), I will take a protein shake. Typically I try to get all my protein from food, with the exception of my post workout shake.