Custom Field Layouts are configured in Setup / Extensibility / Custom Fields / Layout
Layouts determine how custom fields are presented on system entities where custom fields are supported (Accounts, Packages, etc.). Some entities have a 'Custom Fields' tab where the layout will display the custom fields, other entities (e.g. Account Settings) append the custom fields from the layout to existing screen content.
Custom fields need to be setup in order to have fields to configure on layouts.
The Custom Field Layouts panel on the left of this screen allows you to select existing layouts to view and edit on the Edit Custom Field Layout panel to the right.
This panel reflects the currently selected layout. From here you can change add, remove and edit custom fields which are configured for the object in question (account settings, account package, etc.).