The sidebar is a narrow vertical column often jam-packed with lots of information about a website. Found on most WordPress sites, the sidebar is usually placed on the right or left-hand side of the web page, though in some cases, a site will feature two sidebars, one on each side of the main content where your posts are found. This option will create additional left or right sidebars.
Please watch video tour about stisky sidebar option below.
Add widgets from Dashboard → Appearance → Widgets to your sidebar.
Editing page or post select it in "Custom Sidebar" dropdown