How do I add tags to photos in Windows 10?

Select the picture(s) you wish to tag and right click. At the bottom of the drop-down list, choose Properties. Click the tab marked Details, and under the Description section is a category marked Tags. Click to the right of this to get the text box open and add your tags.

For More Information Please Refer: https://answers.microsoft.com/en-us/windows/forum/windows_10-windows_store/apply-tags-to-pictures-with-windows-10/2874e835-b0c6-4f41-a12d-7673048910f8