Basic modes question - What do I do with these things?

[clueless]

I'm new to this mode stuff; *what I'm wondering is how I use these things. *For instance, I've got a book that explains that this mode is for use over this type of chord (example: *Dorian for minor 7th or dominant 7th sus4, Lydian #5 for Major 7 #5, etc.). *

Now, I play mostly rock, so I never run into a dominant 7 sus4. *Most of it is root-fifth chords, or at most triads. *Yet, Plenty of rock players use modes, apparently for some purpose.

So, If I play a I-IV-V progression, do I play the major or minor scale over the tonic chord, and then change to the fourth and fifth modes of that scale over the IV and V chords? *Or is that totally wrong?

I'd like to learn the modes by recording rhythm parts and then practicing changing modes over the various chords, but I can't really get started on this 'till I know what I'm supposed to do.

Thanks,

Jack