Stamina is a classic compressor with automatic make-up gain. It compresses dynamics and can lengthen sustain of just about any recording. Compression is a very popular effect in recording because it gives you a more constant volume in your recording.
Compression turns down the volume of the loud parts while leaving the softer parts alone. For instance, say you were singing and had a great take, but the dynamics are a little inconsistent. You can use Stamina to even out the dynamics of your vocals in a fairly subtle way. Make-up gain turns up the signal after it's been compressed so that it doesn't end up being quieter than the original. Stamina provides this automatically so that you don't have to adjust the level in order to even out the dynamics.
ATTACK and RELEASE are controls that adjust how fast the compressor can control the dynamics. Use small attack and medium release times for cleaner compression, or change them at will to get the effect you are looking for. With low ATTACK and RELEASE times you can start to get pumping and breathing effects which can be fun in the right layer.
SLOPE controls how abruptly the compressor deals with the loud parts of the signal. How compression really works is that it turns down the volume when the signal goes above a certain loudness. The amount the compression turns it down is controlled by the slope. If you want to very subtly control the dynamics, you can use a smaller SLOPE to less aggressively control the peaks. Or you can crank up the SLOPE to just smash the signal down to a constant level.
COMPRESSION is really the major control in Stamina. It sets the volume that you want to start to control the peak level. It is really the loudness threshold that I mentioned above. Turn it up to start controlling the dynamics at a lower threshold.
Like all effects of this sort, you need to use Stamina in moderation to retain some liveliness in your recording. Radio mixes tend to over-compress music to make sure it is always at the same level, but many feel that this takes away some of the life and reality of the music. Remember, the meter in the middle of Stamina will always show you just how much you are compressing the signal. There are plenty of sources that describe how much compression is desirable for specific types of recordings.
