Probably one of the more complicated things to understand about doing dungeons is how threat builds up.

A tanks (usually a Warrior, Druid, Paladin and sometimes a Shaman) role in an instance is to hold the aggro of a mob and often to pull the mobs and direct the other party members movements.

A damage dealers or DPS's (usually a Mage or Rouge) job is to deal as much damage as possible without taking the aggro off the main tank. A good idea is to wait for the tank to have taken about a quarter of the life off the mob before finishing it off. Don't attack a mob that the tank hasn't started attacking yet even if its attacking the tank.

A Healers (usually a Priest, Paladin, Shaman or Druid) job is to heal everyone who needs it and provide Buffs but they usually need to heal the Tank as a priority because if the tank bites it the mob is going to go after the DPS or the Healer next and everyone dies. The healer also has to be careful about generating to much threat as well.

If you are doing a run with a high level player. Stand back and listen to their instruction. If you run ahead and pull all the aggro you will make it hard for them to prevent you from dying because low level players create more threat. If the run goes well they will have enjoyed helping you out and they will probably invite you again.

Also Omen is a good add-on to get to help with knowing how much threat you are generating.

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