new to facebook

When I joined FaceBook, I noticed pretty quickly that I had entered a new culture. I needed some help, and so I turned by email to my sons, my niece and nephew for advice:

To My Closest Advisors

I am in a FaceBook Fog.

Since I'm new to FB, I have some burning questions.

1. I received at least a dozen email notices that "Stephen Bingham has tagged a photo on your FaceBook page." What does that mean? Is it like Freeze Tag? Am I IT? Is that a good thing? Am I supposed to do something? Please advise.
2. The Comment Box: is there FB etiquette for comments? (how do you spell etiquette . . .?) Okay--manners! Is a one-line comment the best thing (i.e. cool)? Can I jump into another comment stream, or is that considered rudely interrupting another conversation? If only one-liners are cool, is there a place on FB for longer conversations, or do we just resort to good ol' email?
3. These Relative designations: how far away from the gene pool do you go? For example, what to do about husband's sister's husband's children by first wife?! Will they feel snubbed if I don't identify them as relatives; or will they feel like I've overstepped my boundaries by claiming them related?

Who knew there would be such sensitive issues to overcome on a public forum for mundane introspection . . .!

Please give me advice on these issues before I embarrass someone who I really am related to and get shunned by a host of new "Friends." :~z

I know I can trust all of you to give me the straight skinny.

Much love--Mom/AuntS