The first thing he covers is the ADSR. That stands for Attack, Decay, Sustain and Release. You can’t learn how to create truly unique sounds using the envelopes in FM8 unless you have a firm grasp on what those terms mean.
Attack is how quickly it takes your sound to go from 0 to it’s loudest point. So a pluck sound has a short attack and a pad, a lot of times has a longer attack.
Decay is how long it takes for the sound to go form the highest point of attack (also the loudest) to the point of sustain. A decay time can be short, like with a pluck, or long.
Sustain is the volume of the sound after the highest point of attack and lowest decay points have been met. So going back to that pluck example, a pluck has a very short sustain.
Release is pretty self explanatory. It’s how long the sound plays for and how loudly after you release a key.
For more helpful FM8 tutorials check out http://http://www.fm8tutorials.com