I have Chessbase 11, so it's probably the same thing.
To add engines, click the Create UCI Engine link at the top, from the HOME tab. Select the exe file by navigating to the folder it's located in, on your hard drive. After adding it, click the Parameter button to change any of the default engine parameters.
I have chessbase 12 and mega database and engines
but i don't know how to attach them to chessbase