You can have as many layouts as you need to for your site, unlike with the other popular blog software.
Layouts can be simple header and footer graphics with or without menus, or complex responsive bootstraps.
If you have a home page that is significantly different than your internal pages make a layout just for your home page, then 1 or more layouts for your internal pages.
You will notice a tab called mobile, if this tab has no content then mobile devices will load the default layout, however if you fill in the layout on the mobile tab cells phones and optionally tablets will see the Mobile Layout. You can choose whether or not Tablets load the default or mobile layout in Admin Options
This screen cast will help you learn to navigate the Layouts UI:
You can click on all Wiki Images to see full sized version