In theory, if you tag posts in your blog by category, those category titles should be offered as links that show a search list of matching posts, on the blog’s main page, in a section labeled “Categories.”
It turns out that, in order for this to actually work, you must first enter values under Settings | Optional | “Category base” and “Tag base” as below. Note I chose to use the value “categories” rather than the suggested value “topic” for both fields. Entering values in these fields will result in the links under Categories displaying a correct listing of the posts in each category: