Tags are labels that you can assign to your talent.
They are infinitely flexible, letting you apply your own taxonomy (or sorting) on the fly.
To assign tags, simply navigate to the person's details (click on their card), look beneath their avatar, and you'll see a line with "+Tag". Click there, type your tag, and press enter on your keyboard. Tag created. (You'll also see a list of all your tags as soon as you start typing.)
Once you've assigned your tags, you'll be able to filter for those tags specifically. Do that by finding the Tags drawer in the Search Filters (either within a team search, or when searching all of your talent).