help with bruiser teamfight tactic

specific example, but general question on tanky bruisers in team fights and how to improve. I was playing garen, I won my lane, but now we were midgame, teams about even in kills. I had mr, hp and armor items with a black cleaver. we lost several teamfights and then the game.

if I engaged their front line, their back line attacked and my team was dead before I also died. if I dived for their carry, I got peeled to death. If I just spinned in the middle of their team, my team died and then I would die.

so, what is my role, in general? should I stay in the front line, peel for my carry, dive for their carry, try to circle around instead of going through their main line?

I have experience with two other bruisers: tanky poppy (who cannot be peeled by others with her ult) and irelia (who has 2 dashes so is harder to peel). so perhaps I just don't get teamfight garen.

thanks