Offlane is often a bruiser role. In a team fight you are in the enemy's face trying to take the damage for your team. At the start of the match you will choose a Health Pot for laning and Green thumb for the armor. Focus on you Last Hits to get gold so you can be stronger and get your cards faster that the opponent.
When laning you can rotate over to the mid lane to help them when your lane is pushed up so that your mid lane can either rotate or back if need be.
With this build you are the one to be up front and dive the enemy team to harass and deal damage. Your role is to harass and take damage while dishing it out. In team fights you are the one to start the fight, and your teammates should back you up or fight others who are dealing the main damage. Be as annoying as you can, get in the enemies face, pull their focus from the ones doing damage to them.