Currently you don't need to enter your passenger information in the Hopper app until you're ready to book your flight. Once you have selected your flights, you will create a profile, where you can enter your name and other passenger details. Please enter the exact name that appears on the form of identification (passport, driver's license) that you will use to fly.
Note that for international flights, you will not be prompted to enter your passport information at this time. You may be prompted to enter your passport information later when managing or checking in for your flight on the airline's website.