1) Essence - spender skills require essence to cast which is a resource on timer, you can speed up essence generation with Empower skills and occasionally get a free essence skill use via filler spells. There are 3 general spender skills as DPS - main AoE spam spell, ST channel spell with big dam and ST instant nuke on CD.
2) Empower Skills increase essence regeneration and decrease cooldown of your DPS CDs - Dragonrage and Deep Breath.
3) Dragonrage and Deep Breath allow you to use 100% of your mastery value and provide big AoE nuke and/or Essence Burst procs from fillers guaranteed.
It works pretty damn smooth.
The gameplay would be to cast Empower Skills on CD (but paced at 8 seconds gap of each other because of Power Swell talent to maximize uptime on essence regeneration buff), then use spenders when you proc burst or capped or need to pump ST or AoE and finally use either of two fillers when you have nothing else depending on spec and circumstance.
You want to fit as many Empower Skills as you can with various CDR talents, so your Dragonrage and Deep Breath CD gets reduced and you can use it again sooner. Then of course you don't want to waste essence/burst charges by sitting on them capped
It's like a mix of Fire Mage and Destrolock.