window.location.href is not a method, it's a property that will tell you the current URL location of the browser. Changing the value of the property will redirect the page.
window.open() is a method that you can pass a URL to that you want to open in a new window. For example:
window.location.href = 'http://www.google.com'; //Will take you to Google.
window.open('http://www.google.com'); //This will open Google in a new window.
window.open() can be passed additional parameters. See: window.open tutorial