OK, if your compressor has a gain reduction meter try this:
Record a fingerpicked acoustic guitar.
Put the compressor in the playback signal chain.
Set the compressor's attack to 10 ms.
Set release to 300 ms.
Set ratio to 2:1.
If it has a knee setting, use hard knee to keep it simple.
For now set threshold to its highest setting.
Play back the recording.
While it's playing, slowly turn the threshold knob lower while you watch the gain reduction meter.
When you start getting a dB or two of gain reduction during the loud parts, that's a very mild, tasteful use of the compressor to control peaks.
Next, set the threshold a little lower so there's 2-3 dB gain reduction happening all the time, more happening at peaks. Now you're using compression as an effect... makes the tone a little thicker.
From there, just exeriment with slight changes in the attack and listen to the differences. Then the same with release. Then the same with ratio.
Tim