Go out, pound your face against mobs. Stay in que as tank. The best way to learn about tanking is to do it. That being said, I routinely see pally tanks doing as much dps as the dps in lower level dungeons. As that starts tapering off, you'll be focused more on using Righteous Defense, Hand of Reckoning, and your other tank tools to worry about your DPS.
*edit* If you are spec'd Ret and queing as tank (I've seen it), please have mercy on your healer and at least equip a shield and 1 hander while you are tanking? Thanks. My baby drood will thank you.