You can add keywords to single files, or to multiple files.
To add tags to a single file:
1) Navigate to the Preview Screen
2) Type a word or phrase in the Tags section and press Enter on your keyboard.
You may use commas or semi-colons to break up tags. Multiple tags can be added at once this way.
The Edit Content dialog opens. Type a word or phrase in the Tags section. You can add multiple tags separated with commas or semicolons. Then press Enter on your keyboard.
When you are finished, click Apply.