Using Writable with Canvas helps you manage your assignments and keep your grades in sync, right inside the LMS your school has chosen. Assignments must be created in Writable, then linked to an assignment in Canvas. Once that link happens, course rosters are imported from Canvas to Writable, and grades go from Writable to Canvas.
Writable should be added as an External App inside Canvas, which should be done by an administrator in Canvas. Read more about how to install Writable in Canvas.