What is a hub adapter? Why buy a hub adapter?
Hub adapters are needed when installing aftermarket steering wheels. You cannot install an aftermarket steering wheel without buying a hub adapter. Hubs are also used to space the steering wheel closer to the driver in some cases.

Does any hub adapter work for any steering wheel? If not, how do you know what hub adapter you need to make any given steering wheel fit?
Different aftermarket steering wheels use different mounting bolt patterns, so you have to get a hub that has a bolt pattern that accord with the steering wheel you want to use. MOMO and Sparco steering wheels, for example, use a six bolt mounting pattern. MOMO and Sparco hubs have 12 holes that are spaced correctly to mount to a six bolt mounting pattern. Grant, on the other hand for example, uses a five bolt mounting pattern. Make sure the hub and your steering wheel are compatible before purchasing. If there is a hub available for your vehicle, then an aftermarket steering wheel can be used with the same bolt pattern. If you're unlucky and your vehicle doesn't have a truck-specific hub adapter then universal ones can be purchased.

How do you install a hub adapter?
An airbag is an explosive device and removal of the steering wheel involves working with it. This procedure should only be performed by a qualified mechanic. If your steering wheel does not have an airbag attached, the job is a lot easier. There is no cutting, splicing, or other kluges required. Your factory steering wheel comes off and the hub placed on your steering column. Once installed your new steering wheel mounts to the hub.