Sometimes when you include a link to an external site, you don't want your visitor to leave your website. In such a case, it might be okay for the link to open in a new window (or tab).
To do this, you need to go into Advanced mode to modify the link manually by inserting target="new" into the link.
For example, you would modify this link: <a href="http://google.com">click here to read this external article</a>
To this: <a target="new" href="http://google.com">click here to read this external article</a>
That's it. Just add the target code and click save.