The only way to book a Southwest Airline flight online is through the airline's website. The airline doesn't sell through third party online sites, such as Expedia, Orbitz or Priceline. Southwest makes its own reservations because the company wants to control price and provide better customer service.
Southwest Airlines can offer lower prices because it doesn't pay Global Distribution System fees, which are needed when offering airline seats through a third party. Its website search engine is easy to use, and the different fare structures are explained under the flexible fares tab. The website offers online check-in with printable boarding passes and has an app for mobile access.