Hi Tia, @AT_24
I apologize for any confusion!
Are you using the K12 Free for Teacher edition of Canvas? If so, then there doesn't have to be an email, you can invite students via their username that they created upon account sign-up.
If you're using them other free for teacher edition of Canvas (canvas.instructure.com instead of k12.instructure.com), then when students or teachers sign up they have to use their email, at least I'm fairly sure with my own experience.
I am a little confused by your question- are you asking how are students able to have an account before you invite them with the link? Students are able to create accounts without being invited to a course if you're using the canvas.instructure.com version of FFT. That is not possible with K12.instructure.com to my understanding.
If you are providing your students with an invite link or join code, and are then asking them to make their student accounts, then they would go to the canvas k12 FFT sign up and make a username, password and enter the course code.
Does this make any more sense? Sorry if it doesn't, please reach out!