Some of these posts may have covered this. I didn't see it, so I'll add my two cents:
These chord forms--major, minor, diminished, augmented--all naturally occur when you derive the chords from a particular scale. If you've mostly played folk, rock, or blues music, which is mostly based on the 1,4,5 (aka I, IV, V) chord progression, you've probably only needed the major and minor chord forms.
(I won't go into how you work out the chords from a scale here, but it's easy to do. If you have a piano or keyboard, it's laid out, right there in front of you.)
A lot of popular music steps away from that I, IV, V zone. A few that come to mind are "American Tune" by Paul Simon, "You've Got It Bad, Girl" by Stevie Wonder, and "Because" by the Beatles, which all reach up the scale and use a diminished chord (or a diminished seven, which seems more common in popular music).