I am new to Twitter and am not sure of the etiquette here.

When others choose to follow you -- should you follow them all? What about Block & Remove -- what does it do, when is it appropriate.

I see on my twitter page that I am following more than are following me which says not everyone follows all their followers (I think of the celebrities -- they can't follow all their followers!)

I see so many "ads" from those I am following; seminars, books, other things they are selling -- is this the purpose?

Just confused by this -- any words of wisdom?