The '2(0)' means you hit for 2 damage but the monster resists 0 points. Monsters (like players) can resist certain attack types. In this case, the monster has 0% resistance to slash. IOW he doesn't resist slash at all. But if for example you were hitting a monster with 50% slash resistance, your damage would be '2(-1)'.
You skill is used automatically (look in used skill, it will change depending on what you are doing). Your feeble damage is to do with various factors, including your low skill level and crappy weapon. At level 5 you will be able to use somewhat better weapons, and your damage will increase.
EDIT:
But if for example you were hitting a monster with 50% slash resistance, your damage would be '2(-1)'.
Or would it be '1(-1)'? I forget, but you see the point.