Most blog platforms let you use a button shortcut for adding a link in a post. You know the drill: you highlight the words you want to link, you click on the Link button, you paste in the URL. Easy-peasy.
But if you want the link to open in a new window, instead of having it take readers away from your page, you can click the "Edit HTML" tab and add a target tag to the link's code.
A link's HTML code looks like this (minus the spaces before and after the brackets):
< href="http://www.exampleURL.com">text text text< /a >
To make the link open in a new window, add target="new" between the URL's endquote and closing bracket. Like this:
< href="http://www.exampleURL.com" target="new">text text text< /a >
If you have a Typepad blog, you can install a widget that makes ALL links automatically open in new windows.