Ok, Black Ops II.
It's a first person shooter, that is, you shoot lottsa baddies and they die horribly.
Every single one of the Call Of Duty Series has been a good game despite various criticisms of each later game as it got shorter and more expensive.
First off, the Xbox 360 controller is the best gamepad for PC gaming bar none. Logitech used to be a contender but they fell behind in the race. I have a pair of Wireless Xbox 360 controllers on my main gaming PC, I have two as most Lego games are designed for two players so this makes it easier to play, having 2 gamepads.
Second off - you don't want to use the Xbox controller for Black Ops II, mouse and keyboard work much better with fps (first person shooter) games. Other games, particularly racing/driving games, will benefit greatly from the gamepad.
So, assuming your computer specs can handle Black Ops 2 (check game manual) load it up. It may need the Steam client to play, not sure. If so, load it up, Steam is ok.
Assuming game is installed and all updated and ready to play, give it a go.
Default keyboard controls are usually ok in CoD games, I use WSAD direction; Space - Jump; C - Crouch; Q - Prone; R - Reload; E- Melee (thump); F - Use; Middle mouse button - Grenade; Mouse scroll - change weapon; Mouse 5 (or any other button) - Run. The Mouse controls direction/Look.
If you're new to gaming it may take you a little while to become oriented with it but persevere. Change graphics within menu to highest your computer can handle and start off at the very easiest level setting.
Good luck and hope you like it
PS: To start and gain experience, just play single player, play multiplayer online when you feel confident enough.