When new bloggers get started on WordPress, they need to understand the basics of what Categories and Tags are. Both can help people find the content they want on your blog, but they serve slightly different purposes.
Categories are big. Broad topics that will repeat again and again on your blog. For example, web education is a topic mentioned over and over again on this blog. It should be a Category.
Under the overarching Category of web education, however, there might be many specific ideas that would be used just once, or perhaps infrequently. For example, a post about web education could be something as specific as how to write good alt text or what ARIA roles are. These very specific topics should be added to the post as tags. Tags are also helpful to search engines in figuring out what a post is about.
Depending on your theme in WordPress, the categories may become part of the menu. For example, on my blog Old Ain’t Dead, I only have 5 categories. These categories are Movies, TV series, Web series, Streaming, and News. These categories are shown as a menu. On this blog, Web Teacher, I have dozens of categories and it would not be useful to list them as menu items. The categories are, however, shown in the sidebar in a pull-down menu.
Blogs can be searched by category. For example, if you select the category blogging from the list of categories on this blog, every post in that category shows up as a search result.
Tags are also searchable, for example a search on the tag alt text. The tag alt text might be used in posts in several Categories, so the search results for a tag would include posts from all those Categories.
Choose meaningful category names. Don’t create category names that convey nothing about your content. For example, category names like “This & That” or “Misc” are not helpful to your readers or to search engines.