You only need to know the address when you program it. Once you program a button for, say P13, that button will always operate P13.
You can program the buttons as pairs, so the top button of a pair gives a P13ON and the bottom a P13OFF, for example.
OR
You can program buttons individually, where each button sends a unique address (10 total) and you then use the on/off/dim/brigh buttons at the bottom to control the device (which is how I'll use it).
You can also make the buttons trigger scenes on scene-capable devices, or events in HS or other software that can respond to an X10 command.