You airline issues the ticket at the ZED fare. Then you contact the airline you intend to fly on and list yourself, stating that you are an interline employee flying on a ZED fare. They will meal list you.
You go to airport, check in as you normally would, if you check luggage, expect it to have standby tags put on it, you wait at check in counter...if your name is called, then you are cleared to security with your boarding card in hand.
In USA, you are cleared through security to the gate with a boarding card with no seat. If you are cleared on board, it is done at the gate, then your bags are boarded, usually in the bulk pit.
Your priority will be the LOWEST boarding priority. Plan on that. Upgrades are at the discretion of the gate agent and based on the policy of the airline relative to upgrades. DO
NOT ASK ABOUT UPGRADES. If you do, you will certainly end up in Economy, if on the aircraft at all.
One last thing, dress nicely. Carry a jacket and a tie. Wear it in the airport on the off chance that they elect to upgrade you. If they don't, then you can lose it onboard. Best to be prepared, since the agents are instructed to select the nicer looking people to be upgraded, so they fit in with the rest of the passengers who are sitting in Business Class.
Oh and on a 3 cabin aircraft, forget First Class....you will almost never see it.
David L. Lamb, fmr Area Mgr Alitalia SFO 1998-2002, fmr Regional Analyst SFO-UAL 1992-1998