To create a hyperlink, select a string and choose Insert ► Hyperlink. Specify a link destination, which can be a cell, notebook, or URL, and click OK.
When you click the hyperlink, Mathematica will jump to the linked cell or notebook.
Cells are targeted by use of cell tags. If your destination cells do not already have cell tags, you must add them first by using Cell ► Cell Tags ► Add/Remove Cell Tags.
To edit the name of a hyperlink, click beside the hyperlink and use the arrow keys to move the insertion point into the hyperlink's text.