You'll find throughout the Help Center we refer to fundraiser participants as "Users", "Participants", or "Guests".  These all refer to people who visit your flight's website or your event.  

As an Administrator or a Flight Manager, you too are a user and may participate in the flight as a donor as well.

There is a Help page for Users if they have questions about how to navigate the flight.

They can visit your flight without creating an account or logging in; however, they will be asked to do so in order to make a donation, buy a ticket, place a bid, or any other activity.