Adding tags to your project files increases discoverability in OSF search.
Open your project, then click the Files tab in the navigation bar.
The "Files" page will appear.
Select a file from the list.
The "File Detail" page will appear. Scroll down the page until you find the "Tags" section on the left.
To add a tag, click inside the box and type your tag, then press enter on your keyboard.
To remove a tag, click the X to the right of the tag.