First of all, you must be editing in Rich Text mode. If you are in Plain Text mode, click the “Rich formatting” link right above the message body box.
Hilight the bit of text you wish to link, then click the link button 
to insert a hyperlink into your Gmail message.
Type or paste the URL of the page to which you wish to link, and click OK.
Gmail will hyerplink the selected text to the document at the URL you enter.
Other articles in this series
This article is part of a larger series on how to insert links into e-mail messages using a variety of e-mail clients and webmail services. Check out “How To Insert Links Into E-mail” for instructions on using links with other e-mail clients.
