The tags are the search tools , should not be confused with the keywords, even though in reality they are not.
Assign one or more tags to a post means identifying with one or more specific keywords that summarize in a sense the topics covered in that post.
Usually appear at end of article, showing in this way the issues addressed in the post and allowing a player to search the blog more items to choose one of those topics.
Let’s take an example to clarify the concept of tags, if you write an article on ‘ install linux the tags allocated might be: installation ,linux , operating system .
The category could be linux, where you have stored all the posts regarding the use of this operating system.
E ‘useless and unnecessary to assign as the tag word linux , since a user will find posts on this topic directly in the category. But if, after reading the post about the installation, want to try other posts which referred talking about the operating system, it will use the tag, clicking at the end of article, the word installation, so you may find your post linux use, for example.
Study carefully the tag before creating them. Do not abuse it because I am a service that you offer to the users of your blog.