Forum tags help you to categorize forum topics, assist in searching and show your users what the forum topics relate to.
There are 2 ways to create a forum tag;
Add a tag or multiple tags when creating a forum topic. To add a description and subscribers go to the Forum Tags tab and open the tag settings you just created.
Open the Forums Tags' tab and click New Tag, enter in the name of the tag and any relevant description, then you may add subscribers to the tag. This will ensure that this topic appears pinned at the top of the users forum list.