Select your text, click on the 
button. In the URL field insert %UNSUBSCRIBELINK% Tag and choose <other> in the protocole field.
If you want to add the unsubscribe link in the html code, you must write it like this : a href="%UNSUBSCRIBELINK%"
To unsubscribe from all the lists, the tag must be : %UNSUBSCRIBELINK%?All=1