To Put a hack into the game you Injector, You can find many of them here on MPGH.
About to add aimbot, you need a hack with aimbot function.
Steps of Injecting a hack/putting the hack into the game:
1- Download an Injector
2- Download any dll you want to hack but make sure it's not detected
3- Run the Injector if you're using windows 7/8/vista
4- Browse the dll
5- Click on Automatic Inject or whatever it's called
6- Write Blackshot.exe/Blackshot depends on the injector
7- Open Blackshot and your dll will be injected.