There are two main stats on your ship
Damage Per Second (DPS) is exactly what it sounds like, the damage your ship does per second when all weapons are active. If you want to see the DPS of individual weapon types, it is located next to the icon of the respected type, Weapons or Drones. Alpha Strike is the amount of damage that your ship will do in a SINGLE VOLLEY if ALL weapons are fired at the EXACT SAME TIME.
This wouldn't be Eve if we couldn't change all the stats of our ship and our opponent's, and we have quite a few options
DPS is changed by a multitude of ways: Stronger Weapons, Modules, Rigs, Implants, and even Ammo can affect your DPS.
For a list of modules and their purposes check out Ship Modules
For a list of rigs and their purposes check out Rigs
For a list of implants and their purposes check out Implants
Your Alpha Strike naturally changes with your DPS number. Alpha Strike is one volley of fire while DPS is a continuous firing of weapons.
While there is no module that specifically lowers the damage output of an enemy ship you can make it more difficult for them to land hits on your ship. Tracking disruptors are an Electronic Warfare module that lowers the tracking of an enemies weapons making it harder for their guns to track you and in consequence, hit you.