To make use of the Inline Grading option you have to access each submission individually.
When you open a submission the document will be opened in the Inline Viewer and you can annotate directly in your browser.
Click on Safe Assign to open the Feedback to Learner window.
To make your comments visible to students click on Submit.
When you click on Save Draft you can resume annotating later and your comments will not be visible to the student.
See also Blackboard Help.