Hi and

to disABILITIES!
The majority of attraction lines in WDW are "mainstreamed". This means that a wheelchair or
ECV will use the regular entrance and line all the way to either a show seating or ride load area. If a line is not mainstreamed there will be signs and/or Cast Members to direct you where to go.
If a show, normally there will be spaces to park a chair or ECV and there will be seats next to the space for other members of the group.
If a ride, usually you will have to transfer to a ride vehicle, although some rides will allow a person in a wheelchair to remain in their chair. If you have to transfer to a ride, and unload is not at the same location as load, your ECV will magically appear at the unload area.
If you click on where it says "disABILTIES" at the top of this page it will take you to the Index. One of the top items is the "disABILTIES FAQ" which will gives lots of useful information. Note that Post #2 discusses mobility and equipment. Post #3 had a wide variety of information and links; it might be a good idea to look at the various park "Guidebook For Persons With Disabilities" for more detailed information.
Or, if you want an easier route, click on the link in my signature.