WordPress tags is a tool that helps make it easier for users to find the content they are looking for on your site. They are often confused with categories, but it is not the same thing. In order to understand how to use WordPress tags, you need to first be aware of how they are different from categories and how people find your content through tags.
Categories are hierarchical in structure. You can have top-level categories with subcategories underneath them. Think of categories as a kind of table of contents for your website. For example, if you have a website about crafts, you might have top-level categories that are named for the different types of crafts, such as "Knitting", "Crochet", and "Sewing". Under "Knitting", you might have subcategories such as "Knitting Patterns" or "Knitting Needles". You don't want your categories to be too specific because your category list would become unwieldy and you would end up with a bunch of categories with only one entry.
Tags...