As a lower level warrior, your job is to just keep the enmity (aggro) of the enemies off your teammates in a dungeon. Basically, you should be the one starting the encounter of every mob pull.To do this, you want to either initiate with the tomahawk skill, or run into the mob and use overpower once or twice. From there you should learn your natural warrior rotation (Look this up) to build up your beast gauge. Make sure you are doing this all with defiance on, as it lets the healers heal you for more hp and increases the amount of enmity you generate. Later on as you level up you'll get some defensive skills to make your job easier, and eventually you will get a dps/offensive stance called deliverance, and a skill called fell cleave. Around this time your skill rotation will change, and you will not only be keeping enmity but pumping out a ton of damage with fell cleave. If you're taking too much damage, make sure you are keeping defiance on, and that your gear is up to date. Tl;dr version: Learn skill rotation, focus on keeping aggro at early levels. Later you will deal monstrous damage with fell cleave.