I got an MXR Super Compressor pedal as one of my gifts from a friend, how do you work these things?
a compressor basically brings your lows and highs more into line so you cut through the mix a bit more.

product description from the dunlop site

"Countless pros rely on the original Dyna Comp to give them the edge in the studio an on stage. Now, the updated Super Comp takes your playing even further, providing an invisible boost to intricate licks, juicing up your sound, and helping you "lock in" like never before. Output and sensitivity knobs let you dial in the perfect setting to keep your parts where they belong in the mix. The new attack level control ensures that initial bite and chunk are never squashed, so you can run the hottest pickups and still hear your dynamics. Create the tight, percussive guitar sound that drives thousands of pop and country hits or add endless, tone-sweetening sustain to your leads. Power: Single 9-volt battery or Dunlop ECB-003 AC Adapter - Controls: Footswitch toggles Effect On/Bypass Output knob sets compressed (attenuated) output level Attack Level knob sets the attack attenuation level (highest attack level is minimum attack attenuation) Sensitivity knob sets the compression ratio (highest sensitivity is maximum compression)"

and the manual...... http://www.jimdunlop.com/files/1145590376_m132_manual.pdf