To link text in the text element, select it. Click the link icon, shown below. (Img. 4.4.1)
You now have four different options. Either create a link to an internal page (Img. 4.4.2), to a file (Img. 4.4.3) in the filelist, to an external URL (Img. 4.4.4) or finally to an e-mail address (Img. 4.4.5).