Tags are descriptive keywords you can add to your video to help viewers find your content. Your video's title, thumbnail and description are more important pieces of metadata for your video's discovery. These main pieces of information help viewers decide which videos to watch.
Tags can be useful if the content of your video is commonly misspelled. Otherwise, tags play a minimal role in your video's discovery.
While you're uploading a video, you'll see a 'Tags' section where you can add your tags.
To add tags to an existing video, visit YouTube Studio and click the title or thumbnail of the video you'd like to edit. Add tags in the 'Tags' box and Save changes.
You can also edit tags on mobile in the YouTube app. Learn how to edit uploaded videos on mobile.