Just confirming what teri said. All the shows and fastpass lines and most of the rides are "Mainstream Access" which means a person in a wheelchair or
ecv and their party wait in line with everyone else, just the same as everyone else. There may be special instructions, like on the Backstage and Animation Tours at the Studio, you are told to stay in a particular line because that line doesn't include stairs. In some cases, the boarding area for wheelchairs is actually at the exit. In most of those, you will still be waiting in the same line as everyone else for most of the wait. You are directed to the alternate boarding area just before the rest of the guest board. Examples of that are Haunted Mansion and The Great Movie Ride.
There are a few rides left where wheelchair users go in an alternate entrance and don't wait in line. There aren't very many of those - Spaceship Earth is an example. For those, the official rule is the wheelchair user and up to 5 members of their party, but if you have 6, they won't make that person go in the line without you. The limit is more for those people who have 20 in their party.
When you get to the parks, you can pick up a Guidebook for Guests with Disabilities at any of the parks. There is one for each park and they give information about where to go for boarding for each ride. For most attrractions, the instructions just say, "proceed thru the regular queue with your party." You can also ask the first CM you see at a ride/attraction. They will direct you to where you need to go.
This link doesn't always work, but it is a link to the official Disney site's main page about disabilities. It should lead you to a place that allows you to download a copy of the Guidebook for Guests with Disabilities for each park.