Opus lets you change many things to do with how it displays the contents of folders - view mode (details, thumbnails, etc), columns displayed in details mode, the sort order, grouping options, and more. Collectively these settings are referred to as folder options. You are able to save sets of folder options for specific folders so that those folders are always displayed in a particular way - saved folder options are referred to as folder formats.
The Folders / Folder Formats page in Preferences is the main interface for configuring folder formats. You can configure several different types of folder formats through that interface:
Please see the Folder Options page for a description of the various options available, and the Folder Formats Preferences page for information on how to configure folder formats.