Please note that throughout most of the options when linking you will see two tick boxes:
Open this link in a new window
Add 'rel=nofollow' attribute
The first option will open the link in a new tab when the user clicks on it, this is espcially useful when taking users away from the site so they still have your site open in the background. This means they can come back to it later.
The 'no follow' attribute option is designed to prevent the link from influencing the search engine index.