Tagavoga - AA is anti-aliasing. The higher the setting, the less jaggies you'll get on your objects etc. This is really important for hair if you want it to look good because a low setting won't produce the look of fine strand hair. When rendering, try to use user setting so you can control the amount of AA you use. I tend to have it high, min 25 -  max 50,  quality threshold 100%. This is for the hair, you probably won't need it this high for other things. Granted, render times will be high.