Hi Gwen- Welcome!
So many questions and so little time! I'll try to do my best and what I don't cover I'm sure the rest will provide the answers.
People get disfellowshipped for alot of reasons. Mostly for fornication or adultery. Although, you would be suprised about the crazy reasons others are disfellowshipped. If the elders don't like you, they will make sure to find something to disfellowship you over. That is an unsaid truth that most jw's would deny, but it's true. They say in their rule books that they will only disfellowship unrepentant people- (buzzer sound) WRONG!
When you are disfellowshipped, your friends and family are no longer allowed to talk to you. If they try and talk to you, they risk being disfellowshipped themselves. Three elders usually meet with you at the kingdom hall when no one else is there and talk to you about your "problem". (Real or imagined) They tell you to go wait out in the lobby while they think about your fate. It's called a judical meeting, and it is very much like being tried in court. Then they tell you the verdict- you're disfellowshipped! Then they read your name after a meeting (like Thurs. night meeting) they tell everyone that you have been df and you hear a gasp then everyone treats you like you are evil and worse then a serial killer. Even your own mom and dad. It's like a death because of how cruel they treat you, you'll never be able to fully trust those people ever again.
If you are reinstated (allowed back in) it's after months or years of going to every meeting and constantly asking the elders to let you back in. (similar to begging) Then everyone acts like they are so happy to be able to talk to you again. But it's not the same after that.
Alot of people try to go back just to have their parents and sibilings around again. But they have to live a phony life. If you're conscience won't let you live a lie, then you will leave the witnesses for good and not have anyone. Not one person from your childhood, not one family member, not one friend. It's a very cruel act for just touching someone's ding-dong.
Anyways, hope that helps!
(sorry I'm in an ornery, crabby mood)