From the course main page, click "Grades".

Click the dropdown and select "Gradebook setup".

Grader report
Grade history
Outcomes report
Overview report
Single view
User report
Gradebook setup
Course grade settings
Preferences: Grader report
Scales
Outcomes
Grade letters
Import
Export

Click "Hide", the same steps can be used to show a hidden grade item. 

For hidden items, this option will say "Show". Select this to release grades to students.

If no "Hide" options appear, the activity has its own setting for releasing marks/feedback that can be used on the respective activity's page. For example, Turnitin has the post date, and Quiz has Review options.

Hidden grade items will appear with a grey name and students will not see it.

Hide a Grade Item