Puncture, the first skill at sword and shield skill line, or better its morph pierce armor. That is the only skill you absolutely need. Keep taunt up, hold the boss still and block nasty attacks and you will be fine. Groupfinder should put low level characters only in easy dungeons nowadays. Rest of the skills on your bars can be defense and self heals depending of your class and what you have unlocked.

When you unlock more skills, low slash the second skill in one hand and shield is great, and you should add crowd control skills like chains if you are a dk to your bar to get adds together for easy aoe damage.

I'm going to queue with my level 11 warden tank, lets see how she does.