What actually happens in the F&I office, and how do I not get rattled?

Picking up a leased SUV soon. Deal’s done, numbers locked in writing.

The finance office is the part that gets me — sitting across from someone who does this hundreds of times a day while I do it once every few years.

For the F&I and car sales folks here: what do you wish customers understood walking in? And what’s the move that catches people off guard most often? Any other general suggestions?