Someone please explain to me how Facebook Group works

Hello friends,

can Someone please explain to me how Facebook Group works, i want to know three things

1. When i create a group, i can add all my friends to the group ( suppose i have 4000 friends i can add everyone to the group ?

2. Can a non-admin of the group add his friends also to the group?

3. How a member of the group gets notified when there is a new group post etc ? since nothing appears on the member's wall

Thanks