What stats determine tank or dps?

[Bellator]

I am thinking of starting a druid and read that feral is easier to lvl up. Having played a shaman, well mostly casters, I see in groups the druids being asked if they are tank or dps. I really have no experience playing a melee character. So what stats determine if the druid is tank or dps? Is one better than the other or is that just determined by group needs?

Thanks

Bellator