infopass is the system that makes your appointment to go and get your passport stamped. It is an online service and you can find a link to in on:
www.uscis.gov.
Once you get you approval email, you can go there, and schedule your appointment. You do need to print it out because you will be asked to show it. 2 things to remember:
1. You need to wait 40 minutes between appointments you are scheduling because their system remembers your IP address. You can do it from 2 different systems at the same time, and get 2 appointments scheduled at the same time or use 2 different browsers.
2. If the systems gives you a meesage in the nature of: "you cannot schedule appointment at this time, please try later" you simply need to try later, it is busy during the day, and better during evening time.
I am not aware of any other use at this point.
Good luck,