Note: This documentation article is specifically for Stella WordPress Theme.
Promo Boxes help you showcase some helpful links or information about your blog in eye catchy way so that users can easily go through the link and avail the important pages in your blog. Like there is a About Me page, or some very popular category which you want your users to explore and here the promo boxes help you much.
To customize your promo boxes navigate to Appearance > Customize in your blog dashboard, there Promo Box > Promo Box 1 and edit the options there.
Be sure you have explored all the options within this Promo Box Customizer section. The live preview on the right will show you a preview of how each adjustment will visually affect your site before you actively apply it.