To book a flight on Frontier Airlines, visit flyfrontier.com or use the Frontier mobile app. Enter your departure city, destination, travel dates, and number of passengers. Select your flight, choose a fare option like Basic, Economy, Premium, or Business bundle, add extras such as seats or bags if needed, and complete payment. For multi-city bookings, select the multi-city option in the search form. You can also book through a travel agent or at the airport, though fees may apply. For assistance, call (844)734-0813. Bookings can be made up to 331 days in advance, and international flights are available to select destinations like Mexico and the Dominican Republic. Ensure all details are accurate to avoid change fees later.