The layout tab is where you choose a layout (or template) and customize that layout to your liking.
This is where you can add new fields and organize them in the order that you want them displayed.
You can drag and drop fields to move them around and also change the direction of how the fields get displayed, such as horizontal or vertical.
By design, a layout can only be applied at the group level. In order to have a different layout for each signature, you will need to put each signature into its own group.