This SharePoint Online tutorial will demonstrate how to create a classic site in SharePoint Online. Note that creating a classic site differs from using the “classic” experience in SharePoint Online. It allows you to actually create a SharePoint site using one of the SharePoint 2013 site templates. While there may be requirements to do this from time to time, Microsoft is expected to deprecate legacy SharePoint sites at some point in the future and so this should be done sparingly or with a plan to migrate / convert to the modern SharePoint Online site.