To link text in the text element, select the text (1) and then click the link icon (2), as shown below. (Img. 4.4.1)
You now have four different options.
Either create a link to an internal page, by selecting the tab "Page", and then clicking the page in the pagetree displayed below. (Img. 4.4.2)
To link to a file, select the tab "File" and click the folder in the folder tree below. Before selecting the file, click the target dropdown above and choose "New window", to make sure the file is opened in a new window/tab. Now click the file to create the link. (Img. 4.4.3)
The link to an external address is created by going to the tab "External URL". Here you can enter the address in the URL-field, and then click "Set link" to apply. (Img. 4.4.4)
The last option is to link to an email address, by selecting the tab "Email". Add the email address in the field and apply with "Set link". (Img. 4.4.5)