To Hit chance is essentially your aim. You try to strike an opponent, or a some sort of a structure that has a distinct Armor Class. In CataDDA, you (dice) roll your chance to hit, add up any bonuses of your own plus your weapon’s, only to score exactly or better than the foe’s AC. Just to be clear, there is also damage resistance (DR), but it works so to decrease the damage dealt by you.
So, essentially, after determining the sequence of action in the current round (a thing called initiative), the game will throw the dice roll for you to tell you if the attack was successfull or not. The weapon speed factor is what should concern you the most.
