Under blog post you can see linked titles to recommended posts - this block displays other Articles that are related by the category and tags.

This feature comes from Template Options > Blog > Details > Related Articles.

If you need a different, more precise solution, just disable that one from the template options, and then use, for example, the Joomla core module "Articles - Related" instead. Joomla module can be published on the "content-bottom" position and assigned to blog pages only, according to the module settings. Joomla core module displays the Articles that are related to the one being viewed by the Meta keywords. All the keywords of the current Article are searched against all the keywords of all other published Articles.