Man seriously don't compare wow private with official. Privates are full of bugs and u ll never learn the real wow there.
Start straight to official.
Well about class there are 3 roles.
DPS [Damage Per Second] [Deal more dmg than the others to kill the mobs faster]
Tank [Hold all the aggro on him] aggro=forces the mob to attack him
Healer [Keeps the party alive]
A dps class i recommend you is a mage. Easy to manage him and deal nice dps.
For a tank class i suggest u paladin, he is just awesome plus he can be healer or dps. Its a hybrid class
For healer you have many choices there. Priest, Paladin,Druid,Shaman can be healers.
So lets sort up each class roles.
Priest: Dps, Healer.
Shaman: Dps, Healer
Druid: Dps, Healer, Tank
Paladin: Dps Healer, Tank
Mage: Dps
Hunter: Dps
Death Knight is only can be created if you have another character to level 55. : Dps, Tank
Warlock: Dps
Warrior: Dps, Tank
Rogue: Dps
Ok for each role you have a specific talent tree. You can start adding talents at level 10.
You 'll mainly focus in one tree and when you get around 60 [ you get the last talent of the talent tree] you can move to another tree or add some points more to your current one.
I started with paladin cause he was Overpowered in Lich King expansion but i ended up playing mage.
Good luck m8.
Dont even try privates, not worths it.