Most blogging platforms let you apply tags to your posts. Tags help organize your blog so both humans and search engines can find what they’re looking for. They’re terms like “blogging,” “SEO” or “Jason’s Weekly Whiteboard” that reflect the topics and content of the post.
Search Engines try to recognize tags and use them to prioritize your site in its search ranking for those terms. The tags are usually links to other pages on your blog (usually a backlog of other posts with the same tag), and like I said in an earlier post, linking search terms to other pages on your site helps too.
So by all means, add pertinent tags to your blog post, but be warned that search engines are wary of sites that try to game this system. They will penalize you in the search rankings if you use so many tags that the web indexing bots suspect you might be attempting to associate your content with unrelated topics just to score extra traffic.
The method for determining this is arcane, but a good rule of thumb is that 5 to 10 appropriate tags are usually right in the sweet spot.