1. Note that it's a "Transfer Switch" and not an "Automatic Transfer Switch"

A Transfer switch is noting but a "BIG Relay" which is designed so mains and utility power CANNOT be connected at once if a part failed.

Emergency panel

If the generator is too small for the house, then you put the loads that need power in an emergency on a single panel. (e.g. refrigerator, sump pump etc)

The "automatic" part might do a number of things such as:
1. monthly/weekly test
2. monitor oil level
3. Exercise generator or generator and transfer.
4. make sure utility power is stable before taking generator offline.
5. Implement cool down phase.
6. The generator exercise period may top off the battery.
7. Monitor voltage/frequency
8. manage starting

So, voltage and frequency out of range will prevent transfer.
Oil level will prevent generator from starting automatically.

You may have two sub-panels and a pool. The pool does not get generator backup.
Looks like your missing stuff like fuses. You may just have a 12 V signal that tells it to transfer. It may or may not need power to keep it in one position.
I did not look at the details.