Welcome to the boards.
You'll find that poly families/networks/tangles form in different fashions. It would be so much easier for us if there were some Official Poly Mating Ritual to engage in to find out how we all fit together. Alas! There is no such beastie, so we have to work it all out for ourselves, every time.
Makes mono dating seem like a cake walk.
I'll suggest just reading the posts and enjoying the variety of experiences that have appeared here in the short time the forums have been up.
And feel free to ask questions. That seventhcrow guy talks a hell of a lot and would probably carry on forever answering questions if you let him!