To find the Layout tab, access your Customizer by selecting Site from the navigation bar. Navigate to the page you want to customize and select the Customize Design button in the section bar, then select the Layout tab.
Layout: Choose between Fixed (you can specify the exact width of your site pages) or Stretchy (automagically fills the available screen space of your visitors).
Margins: Control the amount of space to the top and sides of your page elements.
Sections: On your Entire Site, or if you enable Independent Homepage in the template settings, control the width of the header, body, and footer sections. In other areas—all galleries, all folders, custom pages—you can control the width of the body.
Sidebars: Add content in a right or left sidebar element by turning that element ON.
Pinning: On your Entire Site, or just on your homepage if you enable Independent Homepage in the template settings, pin your header, footer, or sidebar so it doesn't move as the viewer scrolls up or down the page.