Dont be too bogged down on one particular hero. You will do yourself a big favour by playing various roles with various heros. For the first few levels though play a support role, and be the best support you can be .Buy wards, buy courier, up courier. Keep your carries alive and farming and you will quickly build up levels and a lot of commends. Once you get to know the game better then you can switch to a carry role where you are expected to be the damage dealer and big play maker.
Yo don't need that stress when you just start playing - you will lose more than you win if you don't know what you are doing. Spectate some games of higher level players to see where they place wards and how the supports help the carries. We lost so many games because our supports were not supporting it's not even funny. If you do not have vision across the map then you WILL get ganked and your game will be ruined.
Deadman and I make a good team because I let him farm all the creeps and support wherever I can. If he gets in trouble I would rather let them kill me and help him get away than having them kill him because we are going to need him late game.