State Dept website has a place where you can fill out application - it takes you through a wizard to make filling out smooth, error free and you can see the required only information (and not fill out unnecessary stuff). Regardless of first time or renewal, anyone can use this feature.first time passport applicants should NOT apply online ... have to appear in person at any acceptance facility.
All it does is help you fill out information and then give you PDF file that you can print and take to passport facility (postoffice etc). Filling out this way encodes all information as barcode on the application print out so when the agency gets it, they just scan it instead of having to type all the info.