Had an appointment for 10 a.m., got there at around 9:45 a.m. At the security checkpoint I was asked to show my appointment letter (biometrics for AOS and EAD) and my ID. Then I had to put my bag and shoes in the bin and walk through the metal detector while my belongings got scanned. Typical airport-style security.
I then went into the separate office for biometrics, to the right of the security checkpoint. It is a bit confusing because directly ahead is a desk that says "check in here," but it was fine to go directly into the biometrics office.
At the reception there I was asked again for my appointment letter and ID. Then I had to fill in a form with basic information like name/citizenship/weight/height and A-number. Once that was done I was given a number and told to wait until my number was called.
I had brought a book to read (no electronics allowed) but I barely got through two pages of reading when my number was called. My fingerprints and picture were taken and then I was on my way. Overall it took around 30 minutes and everyone was very nice.