Hi Doug,
These are all momentary keys, so need to be held down and used with other things to affect routing.
Holding CH to All Mix shows all the sends for the currently selected channel across the fader strips. It’s the fastest way to send a single channel to multiple mixes.
Holding Assign and using the Sel keys, you can quickly assign or unassign channels from the currently selected mix.
Holding Pre and using the Sel keys you can select whether channel sends to the currently selected mix are pre or post fade.
As these are all to do with routing/sends, I would recommend looking at the mix sends in a routing page whilst having a play with these keys to see what you’re affecting.
Hope this helps!
Cheers,
Keith