Use the charging plate only with the supplied power supply.
Connect one end of the charger cable to the power supply.
Plug the power supply into a wall outlet.
Connect the other end of the cable to the charging plate.
You can keep the plate plugged into the wall outlet even when you're not charging your phone. The plate uses hardly any power when not charging.
Disconnect the power supply from the plate, then unplug from the wall outlet.