VST plugins allow you to have unlimited variety in your sonic palette. They are little computer programs that run inside of a bigger music program like Cubase, Protools, or Ableton Live.
Gating is often used by electronic music producers to chop up long, droning sounds into smaller, percussive bits of audio.
An LFO is constantly going up and down all the time. Depending on your settings, it can raise and lower the pitch, volume, or filter with it.