Low drive means you need a low carrier of 1-2 watts
High drive means you can run a little more, like 5-10 watts into them.
Dead key is the carrier, or when you key up the mic and dont speak into it.
Best way to use it is match the amp to the radio. I.E. a low drive amp is better suited for a Cobra 29/Connex 3300/General Lee. High drive is better suited on something like a Magnum S9.