Once in the transfer chair, the ground service team will pull you backwards down the aircraft aisle. There is usually a small step at the aircraft door from the jetty. This is narrow so it can fit down the aircraft aisle. It has a lap belt and straps to keep you safely secured. They tend not to have much upper body support which can be disconcerting if this is what you are used too. Watch out for the aircraft seat arm rests as you are moved especially if you have delicate skin or prone to muscle spasms.
If you use a walker, it is unlikely you will be able to use this to get to your seat because the aisle is narrow. Instead you will be offered the aisle chair.