Every course you create has a registration status of either Open, Closed or Application Required.
Here is what all of the course statuses mean:
When the status is set to "Closed", no one can register for the course. Once your course starts, you should consider closing the registration.
When the status is set to "Open", anyone can register for your course. If it is a paid course, they must provide credit card information as part of their registration.
When the status is set to "Waitlist", learners can signup for the waitlist. This allows you to gauge if you have enough learners to start your next cohort while still collecting names and email addresses.
When the status is set to "Application Required", the learner must answer a few questions you ask. You will be notified of any new registrations by email and will be able to manually approve each learner based on their answers. Note, that if this is a paid course, their card will be pre-authorized, but not charged on registration. Only, once you accept their application will their card be charged.