The main step when building VST Sound containers is to add VST presets. This can be done using drag and drop, either from the MediaBay or the File Explorer/macOS Finder onto the Content section or the Structure section.
When you add presets via drag and drop, a VST 3 Preset Folder is created, and all presets are added to it.
You can also create a folder for the presets by clicking the Add button 
and then dropping presets onto the folder.
You can create multiple VST 3 Preset folders and subfolders and add presets to different folders. However, a sophisticated subfolder structure is not required, because all presets are later managed via the MediaBay.