I have read that I can add js and css file via .info files. Can I add external css and js files there as well? Eg http://somewhere.com/in_a_galaxy
External JS/CSS files can't be specified in the info file at all. You need to add them via hooks, typically I use
THEMENAME_preprocess_page() for things that need to be included on all pages, or you can use
drupal_add_js() in your
And you can refer to this page. Here you can see how many ways you can add script/css files.