There is some information about the buses on the disABILITIES FAQs thread that should be helpful to you if you haven't already read it.
The older buses have lifts, but most of the lift buses have been replaced with newer buses that have ramps.
Here's how the lift buses work.
The driver will open the back door of the bus for you and fold the seat that is sort of directly across from the back door so that there is an open space for you to drive into.
The driver will stand inside the open back door, collapse the back stairs to form a lift platform and lower the lift. There is a little gate at the end of the lift that stays up (closed) until the lift is safely on the ground. When the lift platform reaches the ground, the gate comes down to form a little ramp. At that point, you will back onto the lift platform. The CM can tell you when you are far enough back - you will also know because the front end of your
ECV will be totally on the lift. Once the lift is totally up and flat with the floor of the bus, the driver will direct you to back into the wheelchair space. If you are not sure what to do, ask the CM. Most are very helpful. The CM will tie the ECV down into place using some belts attached to the floor. There are seats either next to or across from the wheelchair space and you will probably see a sign there that notifies people those seats are reserved for people using wheelchairs or
ECVs. Whether or not you transfer to a seat is up to you, but because ECV users are sitting relatively high in the air, it is safer to transfer from the ECV to a bus seat.
The newer buses with ramps are easier because you don't have to back into the lift. You can drive on. Other than that, the process is the same.
If you can back up in a straight line and turn easily to the right and left, both forward and backward, you should do fine.