First off you have to enable console commands which will be done by changing one setting in the config file. Go to wherever you chose to install Steam then steamapps>common>call of duty black ops>players, there should be a file called config open it up with a text editor(notepad/wordpad). If no such file is found run Black Ops Singleplayer once and the file will be generated.

Once you have opened it up press CTRL+F for search bar to pop up; type in monkeytoy and set the value from "1" to "0". This will allow console commands to be executed in the singleplayer executive.

Adding console commands is the easiest part, you're almost here! Copy paste the following into your config file(anywhere):
bind F1 "map zombie_theater" - this will load your game on Kino der Toten, solo of course.
You simply load up the BO Singleplayer menu and press F1 or whatever keybinds you chose. You can also change maps when you're already playing one. Don't forget if you plan to play on a offline device you need to run steam once with "save my password" while being connected to Internet; then steam will let you use offline mode with no active internet.

Keep in mind you need to own DLCs on your steam account to be able to run any DLC map.