How Do I Know What Scale/s To Use?

[ghettosynth]

Well, the chromatic scale has all the notes, even the bad ones. Then, the major and minor scales take out some of the bad notes leaving you with the basic happy and sad flavors.

I didn't know there were "bad" notes. I will use pliers to pull out the bad notes on my keyboard just like a dentist removes rotten teeth.

That's a good idea. That way you don't accidentally smack them when you're playing aggressively. In their place you can put shot glass holders so you always have whiskey available to keep the good notes, as well as your yourself, moist and flavorful.