I know what project I want to work on.
Find the project using the map, introduce yourself to the group and get to work!
I want to help, but I didn't come planning to work on any specific project.
Use the posted list of projects present to find one that interests you, or to which you think you can add a useful perspective. Then find them using the map, introduce yourself and ask what you can do to help.
I want to work on Project Foo.
Maybe someone else is interested in that project. Find one of the people with an "Ask Me" badge; they will be able to help you find other interested participants if they are here and have likewise indicated their interest in Project "Foo".