First of all, Welcome Jarrick I am sure you will have a great experience playing here.
Now on to some helpful (I hope

) information:
The info provided by diolas is the absolutely boiled down bottom line - as far as group make-up goes. I thought that I would repeat it a bit and provide some definitions (just in case a couple of the terms didn't make sense, heh). Please keep in mind that you will generally not be able to find an optimal group all the time...

and some of the descriptions, etc. are open to discussion and are heavily influenced by memories of live (Game)
TANK - this is a warrior, shadow knight or paladin (in order of effectiveness/precedence)
HEALER - cleric, druid, shaman (druids and shamans are generally backup or spot healers since their healing spells are hard-pressed to keep up with the damage output at high levels - not always though, some players have enough practice and skill to keep up)
SLOWER - shaman, enchanter, beastlords (shaman and enchanter are somewhat equal in effectiveness I think - on live the shaman slows were far and away the best but I understand they are somewhat reduced in effectiveness here on SoD.
CC (Crowd Control) - enchanter, bard, necromancer (enchanters are far and away the best, they have single mob and AOE - Area Of Effect mezzes of fairly long duration. I think the bard's mez songs are pulse based - in other words they refresh every so often and there is a chance of the mob breaking mez on every refresh. The necro's mez is single mob short duration (at least I think so haven't tried a necro here yet)
DPS (Damage Per Second or Damage Dealers) - this is a fairly broad swath of classes, in fact all classes can fit into this category (some better than others, heh). Primarily you will find rangers, monks, wizards, mages, bards, beastlords, druids, and necros here. Each of the primary DPS classes has a secondary role as follows:
rangers - tracking and slowing mob movment (not attacking ability)
monk - pulling
wizards - teleporting to various zones
mages - summoning toys and tools as well as a pet for additional DPS
bards - supreme utility, good at everything, great at nothing
beastlords - combination of shaman and monk (minimal of each) with a pet. Perhaps the only class that does not have a 'defined' secondary role
druids - buffs and teleporting to various zones, sort of a pet
necros - mana battery (can feed mana to the other casters in the group in an emergency)
Here is a site that has a pretty good guide...but more than that it has a link to a ranger site that might be helpful to you...
http://sodguide.game-host.org/
Again, welcome!
Sstecik