An Offsite Facilitation Center has strict security rules since it deals with bulk personal data. You will not be allowed to take your bag or smartphone inside.
The process is very simple and is handled by a third-party company, and there will be no US embassy officials.
Ensure that the details you submit are perfect. A small mistake, such as a slight variation of home address in your passport and D160 form, your surname in all but one document, etc., will lead to your visa getting canceled.
There will be select dates for OFC appointments. So you can expect a small crowd on the day, and plan to reach on time.