libreriadesatoshi.com/entrar isn't a form — it's a fork in the road. You pick your profile and we take you to the right place. You enter your credentials on the next step, not on that page.
The two routes
Section titled “The two routes”I'm a student → takes you to the campus, moodle.libreriadesatoshi.com. There you sign in with username and password, with GitHub or Google, or as a guest.
I'm a teacher → takes you to the instructor space, where you create your teacher account, fill in your profile and propose a course.
If you took the wrong route
Section titled “If you took the wrong route”No harm done — nothing is created or deleted by taking the wrong route. Go back to /entrar and pick the other one. The instructor space also has a Go to Moodle button that takes you to the campus without losing anything you've typed.