Oh ok, ok, I think I get this now. I knew about certain notes like sharps, majors, and chord progression, already. Like how 1-3-5 is a major chord etc. But yeah, I never really delved into scales.
So let me see if I'm understanding this correctly; only notes in a certain scale, usually already predetermined by a midi file, should be used when creating orignal melody, bassline, etc. That's what I'm getting. And the circle of fifths shows you how to read the set scale so you can pick out what notes to use. And if let's say I'm making a new song from scratch, I should pick out a scale I want to use beforehand when composing. I'm sure there are much more things to it, but if that's not the general idea to it, then I think there might be no hope for me x_X