Instructure, the company behind Canvas, has extensive documentation available for all Canvas users. There are guides on all features available to each particular course role:
And there are also guides on the features and functionality of the mobile app.
If you aren’t sure exactly what you are looking for, you can search within particular guides or across all guides. There are also video tutorials available for specific features and workflows.
Here is the link to Canvas Guides: http://guides.instructure.com
You can also use the ‘Ask the Community’ feature, to see if other Canvas users can answer your question.
If you can’t find the answers you are looking for, please send an email to firstname.lastname@example.org.