You will need: Nintendo DS or DS Lite GBA game Method: If there is anything in the Slot-2 of your DS, take it out. Put the GBA game into the DS's Slot-2 Power on your DS Press 'Start GBA Game' on the bottom screen.
No, the GBA slot of a DS is unable to use the wireless capabilities of the DS. You cannot link two DS's together to use the GBA part of the consoles. To do so, you must use actual GBAs and a link cable/GBA wireless adaptor.
The use of the Y Button on a Nintendo DS system varies with the game. Some games will not use the button at all, and any GBA (Game Boy Advance) games played on a DS will never use the Y Button as the original GBA system did not have one.
A DS's Slot-2 (GBA slot) is unable to use the DS's wireless capabilities, even if it's a GBA game which could use the GBA wireless adaptors. You can only use the online portions of a GBA game using an actual GBA and a GBA wireless adaptor.