After students have started to submit their assignments you will have a link to SpeedGrader.

When you click on the SpeedGrader link, a new window will open and the first students' submission will display on the page. You will have annotation tools to annotate specific feedback/comments on the assignment, the ability to type comments into the Assignment Comments box, and the ability to input a score in the grade box. Directly under the Assignment Comments box you also have the option of attaching a file for feedback, creating a video or podcast for feedback, or using the Speech Recognition tool (in Chrome only) to speak your feedback which Canvas will transcript for you in the Assignment Comments box.

When you are done with all of your feedback, click the Submit button. You will see the stats at the top of the page change as you grade, indicating how many you have graded and how many are left. You can navigate to the next student with the arrow next to the student name.