The Tip of the Day screen starts whenever you start GnuCash unless it has been disabled in the GnuCash Preferences. It gives tips on features and using GnuCash. You can use the three buttons at the bottom of the screen to look through the tips.

The Show tips at startup check-box is used to enable or disable the Tip of the Day from running at GnuCash start-up.

It is also possible to configure the Tip of the Day to run at start-up under the General tab in GnuCash Preferences. The Tip of the Day can also be manually run by going to Help → Tip of the Day.