Mears Connect and Sunshine Flyer can be booked on their websites, both companies provide shuttle services between MCO and WDW area resorts. Mears is the larger company that also offers private charters and van/sedans/limos/etc. if you are seeking a more exclusive service or have a large group.
Uber and Lyft are app-based rideshare services, you have to download the apps on your phone and create an account for each service, you request the ride in the app upon arrival at MCO.
A third option is a regular taxi cab, no computer or phone required, you simply walk up to the taxi line at the airport arrival curb and hop on the next available cab.