Hi Kelly - If you're using the Rich Text editor, when you insert your link, there will be a dropdown of "Target" where you can select "Open in new window (_blank)". If you've already inserted the link, highlight the text where you have a link, and click the "Insert/edit link" button in the editor and you'll see the Target option. I've inserted some images below that will show where you'll navigate to.
Alternatively, you can open the HTML code by clicking the "HTML" button. Once in the HTML code, add target="_blank" in your <a > tag. So your whole tag might look like <a href="www.marketo.com" target="_blank" >your link text here< /a>.