What do I do when I get to the testing facility, come on in or let someone know I’m in the parking lot and wait or what?

You have to make an appointment head of time. And you need to be at the facility 15min prior of your appointment.

At the mission office you have to wait outside and they will knock on the window to let you know you can come in. That's only if someone else is at the front desk getting checked in. Yes you do have to have an appointment also