It seems appropriate to resurrect a classic post by Fargo:
This explains concisely everything you need to know about Black Garden and Whitefall Steppes.
Here's some other information that might be helpful:
Quick guide to opponents:
Dude with the thing: priority target. Even if he is being healed still the priority target, cc healers if poss.
otherwise look at the bars.
Green + yellow = warrior, probably riftblade. Liable to run into the middle of 5 of you which is a good time to kill him. Do not attempt to solo.
Green + mauve = rogue. Squishy unless Bards. Bards have hundreds of feminine looking buffs on their buff bar and fart out musical notes. Nuke with extreme prejudice if it's not a bard, ignore unless you have 3+ if Bard.
Green + blue in girly dress - mage. Provided by Trion to give people who think they're cleverer than everyone else a chance to theorycraft. Collect your free kill.
Green + blue in armour. Cleric. Go fight somewhere else unless it's the dude with the thing.