Taverns in Dungeons & Dragons Online are where you go to rest and recover. They often have quests and a spirit binder. The bartender will buy just about anything, sell you food and drink and repair your gear.
While in a tavern or town, you will recover your spell points and hit points. Using food and drink within the tavern will greatly speed up your recovery.
You can find a tavern in the town you're in by looking for a green mug icon on your map.