If you are a wheelchair user and you cannot walk, you will be transferred to an aisle chair to board the aircraft. This allows you to be moved down the aircraft aisle to your seat. There is a facility to strap you onto this chair if your balance is limited. Although airport staff are trained in lifting, they may not have knowledge of spinal cord injury and associated issues. It is therefore important to communicate any particular requirements you have.
If there are steps up to the door of the aircraft, you will access the aircraft through an ambi-lift (a type of vehicle) and into the door on the other side of the aircraft to which everyone else is boarding.
A brochure about travelling through Dublin airport with reduced mobility can be found here