The ACORNS application allows multiple files to be open (active) at a time. In this case, you might need to switch between active files. This is easy; simply click on the name of the open file that shows on the Windows menu.
There are two ways to work with multiple open files. The full view mode is one mode and it is the default. The other is the tabbed view of windows. Using this second view, tabs will appear in the lesson display area for each open file. Just click on the one you want to work with.