Easy-peasy lemon squeezy. Just open your script first please.
Now all you have to do is select "Print/PDF" from the actions drop-down or select the print button from the top toolbar.
This will allow you to create a print preview or download a PDF to print later or send via email. You'll have lots of options according to your desired output: page breaks after each scene, mores and continueds, scene number placement, whether or not to include a title page, etc. It will also allow you to select your print output paper size.