While playing your sound source, experiment as follows:

• Turn the Threshold control slowly up and down. You will hear that as you turn clockwise (effectively lowering the Threshold level) you can hear more of the signal, and also the noise in the gaps where all should be quiet. As you turn counter-clockwise, you'll find that eventually all of the signal is gated out and you don't hear anything. In between there will be an ideal setting where you hear all the signal you want, and all the signal you don't want is cut off. Don't bother writing down this setting since it will be different each time you use the gate.
• Next, try out the Range control and find out why it is set to -80dB nearly all the time during normal gating. This control sets the degree of attenuation when the gate is closed; -80dB is as near as makes no difference to completely off. With lower attenuation settings you'll hear some of the noise coming through between the wanted sections of the signal; this might seem pretty pointless
• in the studio, but it can have uses when full gating sounds too obvious and also when you are 'ducking' rather than gating.
  Now onto the Hold control. If you set this to minimum, you may well hear what is known as 'jitter', and you'll know why from the sound. This happens when the gate can't decide whether it should be open or closed and therefore opens and closes very quickly several times in succession. I know of no musical uses for this sound (yet!). I usually tend to set Hold to around 50mS, or the shortest time I can get away with without jitter, and leave it there.
• Of more importance are the Attack and Decay controls. With these you can shape the envelope of the sound as it starts and finishes, the aim being to transfer gracefully between silence and signal, and back from signal to silence. Get these settings wrong and you'll either hear a little bit of noise as the sound starts and finishes, or the sound will be noticeably clipped. It can take a little time to set up a gate, more if you're using it in conjunction with a compressor, but time spent making careful and precise adjustments will be amply repaid in the quality of the result. Before I move on, I'll just mention that if you're gating a stereo signal, you'll need to press the Stereo Link switch down (it's confusingly labelled). This forces both channels of the gate to open and close at the same time, which is absolutely essential for stereo gating.

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