You have a working copy of DK2 1.3, yes? You can tell what version you're on by booting up the gameand looking at the bottom left of the main menu, it'll say the version number. If it doesn't, that means it's 1.3, which is the only version that doesn't say anything.

Inside your DK2 folder there's a data folder, then an editor folder, and a maps folder in there. Paste the maps in there.

Now to play the levels, right click your DK2 executable and make a shortcut. Then right click and check the properties of that shortcut. There's a bit that says "Target" showing the location of the executable in quotes.

Add the following to the end of it, outside the quotes: -q -level "levelname"

Replace levelname with the map you want to load. For example, the first map in this campaign is "SUPREMACY" so you'll end up with: -q -level "supremacy"

Load up the shortcut and that should load the level. Then you simply need to change the target location for each map.