How To Use the SharePoint App Bar

The SharePoint App Bar makes it easier to discover content and resources in your SharePoint environment, enhancing the overall SharePoint experience in multiple ways.
Everything about SharePoint app bar - Dock 365 blog

What is the SharePoint App Bar?

Along with being an advanced global navigation solution, the SharePoint navigation bar offers an improved content creation experience by providing dynamic displays of custom sites, files, news, and lists. Users can access the SharePoint navigation bar on the left side throughout the SharePoint environment.

Users can view the SharePoint App Bar by default on modern sites. If your organization has not configured the global navigation option, then you will see a home icon first. This icon takes you to the SharePoint start page when clicked. My sites, My news, My files, and My lists are other options available to users.