A little MORE explanation: Save the ( .zip ) downloads SOMEPLACE OUTSIDE of the MAPS folder*, then DOUBLE-click each .ZIP file, one-at-a-time, and DRAG THE file with the .MAP extension ONLY from the pop-up Windows Explorer window into the MAPS folder. (You can then dismiss each popup after the drag-and-drop completes....)
Once completed you no longer need the .ZIP files that you downloaded. (But if you've got the disk space, save them so you can check which version/file you got of that map and from where....)
* Halo CE scans EVERY FILE IN THE MAPS FOLDER upon startup, so having more files in there makes it start up slower, ans slower, and slower....