When you first create and save a + Assessment, you will be taken to the Edit Gradebook screen. From here, you can enter each student's score.
You can also access the Edit Gradebook page by clicking on the pencil within the Gradebook module.
To grade or make changes to your your + Assessment from the Assigned Assessment page, visit the Assessment module and select "Assigned." From here, you will click on the ellipsis located to the right of the desired assessment and select edit.