Not all post offices take passport applications, and some do so only by appointment. Call your local post office, or log on to its website, to find the nearest office with passport services.
Some post office locations offer photo services. If photo service isn't offered, you will have to get your passport photo taken at a seperate location, such as a retailer or pharmacy. You will submit this photo with the application.
You can log on to the post office website and complete the passport application. You can pay the application fee online.
If you need an additional form, like an affidavit of citizenship, you can access this form on the post office website, too. USPS locations do not handle lost or stolen passports or the consent form needed for a child under 16.
If you apply at the post office, the USPS website has a passport status tracking mechanism online.