Your Spaces
For non-public wiki spaces, access is generally determined by your membership in a group assocated with the space. If you do't have access to a space that you think you should have access to, try logging out and back in. Doing so will refresh your group list. If you still don't have access to the space, contact the wiki administrators at congluence-hq@mit.edu.
Using the Wiki
Vendor's User Guide (note that our installation has some configuration and other differences)