NMO is a style of connector, available on different types of mounts. For example, I have a magnet-mount that sticks to the roof with a magnet, and has an NMP connector on top, onto which I screw on the Larsen antenna. An NMO connector is about an inch in diameter, but that doesn't really matter.
You'll need to choose a mount that works for you - either a magnet, a hood lip, or maybe a roof mount that you would have to drill an actual hole for. An in-roof mount provides the best ground plane, but if you're like me and don't want to put a hole in your roof, a magnet mount is a good alternative. Just be aware that that antenna is about 3 feet tall, and can get caught on low-handing brush. If that's a concern for you, you might want a rubber duck style antenna with an NMO mount. They're shorter and more flexible to avoid hangups, but have a little less RF gain.