Attacks are the meat of the combat turn. An action's success or failure and potential impact on the target are determined at this stage. You use a certain Attribute/Ability combination depending on the type of combat in which your character is engaged:
Close Combat: Use Dexterity + Brawl (unarmed) or Dexterity + Melee (armed).
Ranged Combat: Use Dexterity + Firearms (guns) or Dexterity + Athletics (thrown weapons).
Remember, if your character doesn't have points in the necessary Ability, simply default to the Attribute on which it's based (in most cases, Dexterity).
In ranged combat, your weapon may modify your dice pool or difficulty (due to rate of fire, a targeting scope, etc.); check the weapon's statistics for details.
Most attacks are made versus difficulty 6. This can be adjusted for situational modifiers (long range, cramped quarters), but the default attack roll is versus 6. If you get no successes, the character fails her attack and inflicts no damage. If you botch not only does the attack fail, but something nasty happens: The weapon jams or explodes, the blade breaks, an ally is hit.
See Modifiers and Maneuvers to see the alterations to rolls depending on each.
You can also abort an action at this time.
