Child themes are standalone themes that inherit most of their functionality from a parent theme. When using a child theme, WordPress prioritizes the child theme’s features, falling back to the parent theme if a specific function isn’t found. This approach is ideal, as it lets you customize only the elements you need while keeping the core functionality intact.
Child themes should always be used if you plan on modifying even a single character in your theme.
If you plan to edit the theme files, like style.css, we are suggesting you to install both fanky.zip and fanky-child-theme.zip themes, then activate the child theme. Child themes are great because allow you to edit the theme and also lets you update the original theme in the future, without loosing your edited files work.
More about child themes and how to use theme you can read here