Shaman's in EQ2 are healers. The DPS classes are Mage and Scout. Tanks are, well...tanks.
You can 2-box with any 2 classes as long as you have a healer. If you want to kill things fast, go with a DPS class and healer. If you want to take on very hard mobs, pick a tank and healer.
Of the healers, here's how they basically do business:
- Cleric: Large single heals and can wear plate armor.
- Druid: HoT and buffs.
- Shaman: Wards and debuffs.
Each has a sampling of other abilities, but thats the basic idea.