There is no "rule" that you must arrange for a skycap prior to your arrival at the airport, but noting in your reservation that you will need wheelchair assistance ahead of time makes it easier (I've found) when you get to check-in.
Most airlines have a button you can click on ticket purchase to indicate special services needed. If you did not set this up in your original reservation you can call the airlines at any time and have them note it for your particular need.
When you get to the check-in counter at the airport just let the attendant know that you requested a wheelchair and will need a skycap. Usually the skycaps are not airline employees, rather they are from a contracted company that the airport hires and each airline uses. Some will allow you to request a wheelchair only (no pusher), but many require you to have a pusher also (which pretty much means a forced tip). The skycap will pick you at at (or close to) the check in counter, take you through security, stop at the restroom if needed, and deliver you directly to the gate.
Sometimes they will try and take the wheelchair away at the gate leaving you to sit in a regular chair. If you are unable to walk down the jetway unaided, ask that they leave the chair there for you so you can safely board the plane. Also, if you want to wander the airport (go shopping, get food, use the restroom again, etc) you will want a wheelchair for that.
When your flight is ready to board you should be allowed to pre-board. Line up in this line and someone will assist you down to the door of the plane (either a skycap who has come back to assist, or an airline employee). You will then get situated in your seat. Make sure to let a flight attendant know that you will need a wheelchair at your destination or any connecting airports. They should contact the destination airport prior to your landing to arrange for this.
About 15 min or so before landing make sure to remind the FA that you will need a wheelchair so that they can contact the airport if they haven't already done so. When your plane lands you will be the last to get off. There should be a wheelchair there waiting for you, if there isn't, DON'T get off the plane until one is there. Many times if a chair is not there and the person chooses to go to the top of the jetway, they are then forgotten about. Make sure you get the help you need from the beginning!
The skycap will take you from the plane door to the restroom (if needed), and down to baggage claim (or ME if you don't need to go to BC b/c the bags are tagged).
My recommendation is that if the person can not walk from the car/drop off spot to the check-in counter, that you rent a wheelchair locally to take with you on your trip. This will save a lot of hassle on the trip b/c of walking distances that you are not used to. If you are renting an
ECV and having it delivered to the hotel, that is fine too. I wouldn't expect a Skycap to be available at the curbside drop off area in the blink of an eye, or for the curbside bag guy to be able to locate one quickly. In my experiences the check-in agent always has to page one over the loudspeaker, and then it takes a while for them to come.
Depending on how many legs to your trip you have, make sure to have singles with you for tips. Let the service you receive dictate how much you tip. If the person shows up quickly, is kind, polite and able to carry on conversation (or not if that is what you desire), helps with what is needed and takes you to the "extra" places such as the bathroom and to a news stand to buy a pack of gum, $5-7 would not be unheard of. If the person is slow, rude and only does the minimum $1-2 (or none and make sure to file a formal complaint). Remember this is for EACH person who pushes you, so if you have your original flight, a connecting flight, and the destination, that is 3 tips that day. I would then carry between $15 and $20 in singles if possible. Many times the skycaps are paid very little and rely on the tips to make ends meet (often they are paid like waiters/waitresses where they make less than minimum wage and make up for it in tips).
Good luck and HAVE FUN!
Mandy