DoN is a lot of fun. It all starts as you may have figured out in Lavastorm. Invis and lev up if you are lower level, or just wander around. As well as normal lavastorm components, you'll see some npc folk near the centre of the zone (various races standing near a gypsy van). You can hail them and start your jouney. You will be given small quests to help you raise faction. (There are no crystal rewards). You have to choose the dark side or the good side at this point.
At the same time, if you have friends or a guild, you can join parties doing group tasks and start earning cystals and further faction.
When your faction is up (read the details in links from the Zone on this site)... head into the tunnels. These have a "good" side and camp and a bad side and camp, and meet in the middle for a zone in to the next area. There are maps available for download. There are both normal zones, and instanced versions of normal zones.... a neat idea indeed. You can start your "progression" for DoN as this time, with a sequence of tasks solo and group that earn you faction and plat. As you go through the progression (a separate part of DoN from the group quests) you will actually earn AA points and special AA points (that grant you additional stats). At higher level you earn DoN only spells.
The crystals can be bought and sold, earned in tasks and group tasks, and also changed in at the DoN merchant in the tunnels for some VERY nice items indeed.. Shaman Panther spell, for instance, very interesting augs, and good armor.
So its a bit like LDoN, but a better overall system. You can treat the zones as ordinary zones and just go and hunt there. You can also trigger tasks that mean you zone into the same zones but they are instanced for you. You can get some nice gear, but can also sell and buy the crystals (which are otherwise like the LDoN points).
Hope that helps a bit.