If you mean Same Day Confirmed Standby, (which I have changed your thread title to,) in the aa.com page is here (link) and in the link previously posted.

In part, it states "When you want to confirm a flight change before arriving at the airport, simply call our Reservations desk at 1-800-433-7300.

Our Reservations staff will provide a choice of available flights departing no less than 1 hour and no more than 12 hours from the time you call. The $25 fee* can be paid over the phone with a major credit card."

and

"*Note: Passengers traveling on unrestricted fares (Y, B, H) and AAdvantage AAnytime travel awards have the flexibility to change flight arrangements at no charge..."

If you are addressing issues like route changing, that might depend on the fare rules - your friend might have a higher-cost fare with more flexibility (and no $25 fee if it is Y, B or H) than you have. It will still depend on seat availability, AFAIK.