Time to exercise my fingers.
Attack: How fast compression reacts and starts to kick in.
Threshold: The level you set to react, so the compression will start at this point you have set.
Release: How much substain you want when the compression reacts.
Soft/Hard Knee: How you want the compressor to lower the levels. In a subtle way or a forceful way.
Ratio: How much compression you want, 1:1 up to infinity. The higher the ratio, the more your output will be reduced. If the ratio is set at 2:1, that means that for every 2db change of signal level above the threshold from the source input, the compressor will only output a 1db change.
Output Level: To compensate for any loss of levels during compression.