Instructors can view, input, and edit grades using the Gradebook by clicking on the Grades link on the left-hand navbar. The Gradebook will break down students' grades by assignment, assignment group, and total course grade. This data can be sorted and filtered according to various metrics.
The Gradebook is also where you can modify the Late Submission policy for your course. To do so, click on the cog icon at the top-right, and then select the Late Policies tab. The Grade Posting Policy tab will allow you to switch between automatic and manual grade posting.
For more information on the Gradebook, check out the Instructure Help Pages.
Another method of inputting grades is SpeedGrader. This can be accessed one of two ways, from the Gradebook or directly from the Assignment. SpeedGrader allows you to view individual submissions, attach annotations, post comments, and grade assignments all on one page. It also allows you to grade via rubric, or check for plagiarism using Unicheck.
More information on SpeedGrader can be found at the Instructore Help Pages.