Here is a quote from chess.com about it
"The tags are associated with the puzzles through a voting process. Vote for a particular tag by clicking on the "thumbs up" icon, or by selecting a tag from the "Suggest tag(s)" drop-menu. You can vote against a tag by clicking the thumbs-down icon. As more people vote, the tags grow smarter and more relevant.
A premium membership is required to vote for tags. For each puzzle, you may vote only once for a particular tag, but may vote on as many different tags as you like."
I hope this helps :)
When you finish TT problem, you see a list of themes, such as Hanging Piece, Mate in 3+, or Interference.
What happens when you give them a thumbs up/thumbs down? How can you get rid of bad themes? What happens when you suggest a theme?