Hyperlinks are generally thought of as connections to a web page, but they can be used to connect to any kind of file e.g. Word or Excel. MS Project allows you to create hyperlinks on tasks, resources and assignments.
When project plans contain hundreds of tasks or resources hyperlinks to other tasks or resources can be very useful. For example a hyperlink could you take you from a task to it's assigned resources or could link from a design task to a related prototype task. You will need the task or resource ID of the task/resource that you want to link to.
To edit an existing Hyperlink right-click the task or resource. In the menu select Hyperlink.
You can then choose to Edit Hyperlink, Copy Hyperlink or Clear Hyperlinks.