To add a blog template in WordPress, navigate to your admin dashboard and click on Appearance followed by Themes to add and activate a design. If you want a custom layout for your blog posts, you can use site builder plugins like Elementor or the native block editor template builder. Go to Site Editor under Appearance, select Templates, and create a new single post or blog home layout. Once you publish your new template, all your blog posts will automatically use the updated layout structure.