We took 4 cruises with Royal Caribbean out of LA this year (I assume you are going on Navigator of the Seas?). My wife needs wheelchair assistance to board and disembark. The info kokopelli-az provided is mostly accurate. You should ask one of the port employees to point out the exact location to you, but basically there are benches in front of the building entrance where you will seat and wait for someone to come and get you with their wheelchair (unless you are coming with your own). That area is by the small white tent in front of the building, close to where you drop off the luggage and where the lines to board form.
There will be two people helping you, port employee and then Royal Caribbean employee as kokopelli-az mentioned. Port employees pushing are not allowed to assist you with luggage (labor union issues). They will not even touch your bags. So you need to be able to handle all carry-on.
They will help through security and gangway onto the ship. They will not take you to your cabin. Our cabin wasn't ready when we boarded, so it wasn't really an option. In our case they left us at Bolero lounge, close to the rear elevators. After that it was up to us to figure out how to navigate the ship. My wife can walk short distances with her cane, so we managed.
For disembarkation definitely let them know you will need assistance so they will put you on the list. We had to go to the same Bolero lounge to wait for the wheelchair assistance. It was reasonably quick. It's also the same process with two people - Royal Caribbean crew member will take you off of the ship to the port and will "hand you off" to the port worker, who, once again, is not allowed to touch any of your bags. They will get you outside of the building. In our case we were catching Uber, so they got us to the island where you wait. There are no benches on the island, but there are benches by the building, Depending how long you need to wait for your transportation, you may want to ask them to leave you by the benches. You'd just have to cross the road to get to the island if needed.