Workplace Medical Insurance (How does it work?)

Hey all!
This is my first time getting medical insurance through my employer but I have no idea how it works. I've been enrolled in the Silver 70 HMO plan since July 1st. However, I haven't received anything in the mail or email. I called Kaiser today and they couldn't find me in the system. All I have is a group number.

Can someone explain to me how employment-sponsored medical insurance works? How do I go about using it?