To make it simple...
You hit the monster, and the monster hits you. Then you hit the monster, and the monster hits you... etc. If you\'re faster than the monster, you hit the monster more than the monster hits you, yet if you are slower, the monster hits you more. If you have dodge skills, the monster might not always hit you, and if your attack skill is not good enough, you might not hit the monster. If you wear armor, the monster does not deal you the same amount of damage, yet if you\'re not strong enough, the monster might not take damage from your hits.
If that doesn\'t make sense, you should wait until you\'ll experience fighting in the game.