Goen, Here's something you can do to see how modes work, record a G-C-D chord progression, play the G Major scale over it, now take the C Major scale and rearrange the notes,so that G is the root,GABCDEFG, play that over the G-C-D progression, now take the D Major scale& do the same thing so you have GABC#DEF#G, play that over the chords, see how it works, same Root, same Key, different Mode, some modes will sound good, some not so good over the same chords, I had the same misunderstanding about Modes, but when it's put in the perspective of playing over some chords it made sense, OK, now go do some experimenting with some songs you already know, and play some different modes over them