The tags for your blog profile are automatically generated by how your followers have categorized your blog. As you gain more followers, the more tags that will display and the more accurate they will be.
Tags for specific posts are determined by how they are categorized in your RSS feed. Howe you can manage your post's tags will depend on what blogging platform you're using. Here are some guides for edit posts for some popular blogging platforms:
There is not a way to manually add or remove tags from your blog at this time.