You can access previously opened worksheets through the worksheet hyperlink history icons (arrows) in the Home tab of the ribbon if the previous worksheet has been saved.

As an example, open the examples/Calculus1Visualization page, and then click a hyperlink to another example worksheet, say, Tangents, Inverses, and Sampling. The new worksheet opens. To return to the previous page, click the back arrow icon.

Note: You may be asked whether you want to open a hyperlinked page in a new tab, in a new window, or in the current window.  You can always change this setting in Options>Interface.

Use the worksheet hyperlink history icons (arrows) to go back and forth between links within a worksheet.