The druid class is something of a jack of all trades, but in a different way than the shaman. Like the shaman, it incorporates melee abilities into an offensive/healing spellcasting class, but instead of including totems as a way of buffing your party and debuffing your enemies, the druid is able to shapeshift into bear and cat forms. In effect, this allows the druid to take on the role of either a warrior tank (in bear form) or of a rogue damage dealer (in cat form), in addition to the secondary healer/offensive spellcaster in your humanoid shape.
Of course, there are some limitations to these abilities, the most telling of which is that you can’t cast your normal druid spells while shapeshifted. You’ll only have a few core abilities to use while shapeshifted, which are generally similar to those of the classes that the shape matches; the cat form even uses the same combo point/finisher system as rogues do. Of course, you shouldn’t expect to be quite as good at the warrior or rogue roles as an actual warrior or rogue would be - you don’t get any skills that correspond to the Taunt or Sap abilities of those classes, for instance - but you can still stand in for one of them in a pinch.