Do I need app if I didn't get registration ?

Right now DMV is only catching up on previous appointments, but you dont need an appointment anyway. You will get in line outside and a staff member will give you a sheet with a number then when you get near the door another staff will take your info and tell you to wait in your car until you receive a text message to go inside. Once inside you will wait for your number to be called, and the whole process will take about an hour.

You do not have to an appointment, but anyone without an appointment may expect to wait 2 hours or more at peak times before you are served at a counter inside. Try to set an appointment on DMV site online, but the appointment system was down when I tried.

No, you don't. You will get a text message when your documents are checked outside and when it's your turn to go inside.