Prepare for arrival:
Disarm doors, which actually means to set the evacuation slides to manual mode, because in automatic which is used during flight and taxi, the slides would pop out on opening the doors. Happened before and can cause serious injuries if not even death to rampers.
Cross Check - this is used all the time when flying, for example during the last checks before the flight the pilots perform cross check to ensure they both went through all items of the checklist. It means basically, that 2 or more people confirm to each other that things are done. I think even the 80 knots announcement sometimes was/is made as "80 - crosscheck" to make sure that PF
and PNF both have the correct speed indicated. During arrival checks, the FAs confirm to each other that the doors are manual and safe to operate/open.
Stand By - just simply wait...for whatever...
All Call - mentioned before, this means that the crosscheck is performed on the intercom by all FAs at their assigned doors. Smaller planes only use front doors, then the crosscheck is performed across the aisle.
So, if you are an FA
and that command is yelled into the PA, you go to your assigned door, set to manual to disarm the automatic slide deployment and you use the intercom to check and confirm with the otehr FAs that slides are disarmed and the doors safe to open now. After all have crosschecked you open the door and the pax can disembark.
Side note: I am no airman, I learned that here and from books and videos, stand to be corrected...