How to Use and Create WordPress Tags
If you have an established WordPress blog with categories already created, you can convert some or all of your categories to tags. To do so, look for the Category to Tag Converter link on the right side of the Categories page on your WordPress Dashboard. Click it to convert your categories to tags.
Tags are not to be confused with categories, but a lot of people do confuse them. Tags are clickable, comma-separated keywords that help you microcategorize a post by defining the topics in it. In contrast to WordPress categories, tags do not have a hierarchy; there are no parent tags and child tags.
If you write a post about your dog, for example, you can put that post in the Pets category — but you can also add some specific tags that let you get a whole lot more specific, such as poodle or small dogs. If someone clicks your poodle tag, he finds all the posts you’ve ever made that contain the poodle tag.
Another reason to use tags: Search-engine spiders harvest tags when they crawl your site, so tags help other people find your site when they search for specific words.
You can manage your tags on the WordPress Dashboard by clicking the Tags link on the Posts menu. The Tags page opens where you can view, edit, delete, and add new tags.