You now have two tabs open on your screen. 
See the two index labels just above this page?

"New Tab" is highlighted because this is the page you are reading. 
NOTE: your back button is grayed out.  It will not bring you back to Mousercise.
This is a new tab that has no history.

Clicking the tab for "Mousercise 5 W2 Juggling..." will bring that page to the surface, burying this one. 

You can easily bounce back and forth between the pages by clicking their tabs.

You now know how to juggle windows!

When you are finished playing,
close this extra page by clicking the Close Tab "X" on the tab.

CAUTION- do not use the X in the red box in upper right corner-
that X would close all tabs, and you would lose your place.