The sidebar is content that you can find to the right side of your Gmail.
Addresses, Packages, and other links
When you open a message that lists an address or package tracking number, Gmail shows you handy links to maps and directions, or your package's delivery status. These links are produced automatically for your convenience. No humans read the content of your email in order to generate these links and none of them are sponsored by advertisers. We hope you'll find them relevant and useful!
Add to calendar
Gmail displays an Add to calendar link when you open a message that contains event information. To add the event to your Google Calendar, click the link and fill in the appropriate information, then click the Save Changes button. (You may be asked to sign in to Google Calendar, if you're not signed in already.)