I’m only just learning my way around the OP-XY, but I will try to explain. Someone please correct my terminology if it’s incorrect.
Pressing the Arrange button puts you in Arrange Mode for a single Scene.
The big number in the center of the screen indicates which Scene is in focus. Holding shift and pressing one of the accidental keys will bring a new Scene into focus.
The small number at the top of the screen indicates which track is in focus. Pressing any one of the track buttons will bring that track into focus.
Each track can hold up to nine Patterns. The number buttons below the window, show what you can do with the Patterns on a track. If there is only one Pattern on the track, the options are: new, copy, paste, clear. If there are multiple patterns on the track, the options are: new, copy, paste, delete. You can scroll through multiple patterns on a track using the number four encoder button.
Once you have a Scene in focus, you’re free to switch to instrument mode and select instruments and record notes on any track and they will get recorded into the Pattern that was in focus on each track in the Scene that is in focus. In this way, you can have up to nine patterns on each track and each pattern can have its own instrument and its own notes.
From my understanding, this is different from Song mode. You enter Song mode by holding shift and pressing the Arrange button. In Song mode you can sequence the Scenes that you have created. You have to hold the shift key to activate the number buttons below the window. With the shift key pressed, the accidental keys, allow you to add Scenes to the song that is in focus and the natural keys allow you to bring one of 14 songs into focus.
Something new that I learned today is this. If while, you are in Arrange mode, you hold the shift button, the number buttons below the window show what you can do with Scenes rather than Patterns. The options are: clone, copy, paste, reset.
I hope this helps.
Rick