Yes - it does suck at teaching how it works.
Reading the tooltips for abilities I kind of get which are for dps and CC and which are to apply debuffs or for tanking/threat / damage mitigation, so that's ok.
WS-Base.com is a decent website with info. I haven't delved into guides for classes / roles / stats to stack for those roles, but the game doesn't tell you what gear stats are good for what class / role.