Workflow question

Have a GO coming this week and just trying to understand the single boiler workflow along with how it functions in regards to steam, filling up, pressure, etc.

At what points do i need to purge water through the group head? My understanding is:

Once up to temp and before pulling a shot - releases pressure in boiler and heats up lines?

After shot - just to clean group?

After steaming milk - releases pressure in the boiler again and refills water?

Appreciate any advice or tips