We include How to Wiki on the welcome page of every site. This should be our best ready help but it is old and often fails to offer the best advice. We'll work on this one page a day.
Here we describe how to use the web interface to the federated wiki. Read About Federated Wiki to learn about the project. If you are just starting to write in your first wiki then read the Field Guide to the Federation.
Next up:
How to Find Sites that share with you.