The Emails (Atlas) web part is a pre-configured In Focus web part which shows the latest emails relevant to the page. The screenshot shown below is using the default layout "Carousel":
Each tile shows the name and date of the email, the file icon and a preview of the email. Users can click the title or image to open the email, or use the arrows in the top right to page through the available emails. Click the ellipsis (...) in the bottom right to see additional options:
Emails can be uploaded via the Add It wizard. See how here: Add a Document or Email using Add It
Edit or Delete existing Emails
To Edit or Delete Atlas content please check this article: Edit or Delete Atlas content. Please note that emails are stored in the Documents library.
You can customise the layout and query of a Documents web part by editing the page, then editing the web part and modifying the configuration options. All the configuration options for In Focus web parts are described in the linked article: Configuration for In Focus web parts