Hi Vicki,
I'd like to explain that the Frequent sites shows the SharePoint sites you visit frequently or, if enabled by your administrator, a list of recommended SharePoint sites generated by the Microsoft Graph (Office Graph). Recent activity information about this site will be displayed in addition to the site name and link.
Office Graph is an underlying service running on Office 365. It is designed to securely capture key interactions between actors (users) and objects (documents and other contents). For example, if I view a document, that interaction gets stored by the Office Graph making that information available for applications (like Delve) to create powerful experiences. We can enable it by allowing access to the Microsoft Graph in the Office 365 admin center.
Regards,
Joanne