This tab can be used to modify the layout of the currently edited alternative form. If you check the Use custom form layout check-box, the familiar CKEditor will be displayed, enabling you to create a custom form layout. Clicking the Generate table layout button above the editor will generate a default table layout containing all visible fields defined on the Fields tab.
Detailed information the Alternative forms module is located in Developer's Guide -> Modules -> Alternative forms.
Page url: http://devnet.kentico.com/docs/6_0/contexthelp/index.html?alternative_forms_layout.htm