User Guide
Manifold is a very user-friendly piece of software and most features should be pretty self-explanatory. Still, it may save you some frustration to watch these short instructional videos first.
Videos
Tutorial Students
Tutorial Instructors
Documentation
If you prefer to read, Manifold also has written documentation available on their website. I'd recommend sticking to the "Using Manifold" section.
Help
If you (an instructor) need additional support, you can contact support@trialanderror.org