New unread mails are marked in bold. You are also notified in your browser tab like this: The number (1) corresponds to the number of new mails. So here, only one new mail.
By clicking on a mail, it opens on the right side. You can view it in detail. You can see : the sender, as well as the recipient (s). For mail with attachment: by hovering over the name of the attachment, you can preview it. Click “download” to archive it on your computer, “briefcase” to save it in your briefcase, or remove if you want to delete the attachment.