Can you explain the layout functionality?

Our invoicing software gives you the opportunity to select between a range of predifined templates, styles and variations. The settings are structured so that changes done to the "Base Layout" will apply to all other layouts. 

You can change the texts used on the documents, choose which columns should be visible, specify a background image (typically your company letter paper) and logo. Also choose between our templates, header templates and styles.

By default all layout settings inherit their settings from Base Layout. That is what the "Based on" field indicates.