When you go to http://familysearch.org/ you find Family Tree as an option. Anyone can join the tree.
The FamilySearch techies are preparing for two million new users in the next two years. Hopefully the servers won't be blown out by a bigger surge of traffic than anticipated. We think it will be fine.
Family Tree is pretty intuitive, with some things you need to figure out. My opinion on the best way to learn tree is on Elder Moons site: http://familysearchtraining.com/
Note: It's one tree for all mankind. You will be seeing stories, photos, documentation uploaded by common relatives.
You can discuss. We are all building one tree. Lets be nice and work together. Yes, no more wasted effort and duplication of research, research repeat.
This article gives an insight on what will happen when a new patron logs on, and are likely to only have their name in the pedigree. Click here