You don't have to charge for your LessonFlyer courses. You can offer courses for FREE to students.
In fact, when a new course is created FREE registration is the default enrollment type so you don't need to anything to setup this option.
Although your course is free lesson content is still password protected. Students are required to register by completing a form that asks for their name, email and to choose a password. After enrolling they'll need to sign-in to your course website in order to view the lesson material.
Please note: At the time of this writing we do NOT currently have a way to publish a free course that doesn't require registration. I.e. where lesson content is freely available on the internet without login required to view it.