You shouldn't have to import anything. The Lightroom files are platform-independent, so it should just be a matter of moving and relinking them.
- Copy the folder containing your Lightroom catalog and previews to a location on the iMac (such as in the Pictures folder).
- If the photos themselves are not inside the Lightroom folder, copy that folder to the iMac too.
- When you first start up Lightroom it will probably think all the photos are missing. In the Folders panel in the Library module, find the topmost folder containing your photos, right-click it (if you turned on secondary click for the iMac mouse or trackpad, otherwise Ctrl-click that topmost folder), and choose Find Missing Folder. Locate and select the topmost folder containing your photos where you put it on your iMac, and Lightroom should link them all back up.
Because you have copied the entire catalog to the iMac, all your collections and metadata will be on the iMac.
Now, because you're moving from Lightroom 5 to CC, it will probably ask to upgrade that catalog too. Be sure you give the upgraded catalog a name you recognize, so that you don't accidentally open the old catalog again or it will ask you to upgrade it again.