In the explanatory pop-up for "Como se prepara una tortilla de patatas:" https://spanish.kwiziq.com/revision/grammar/expressing-instructions-and-general-statements-with-the-impersonal-se-one.
I'll spend some time on this exercise because I find these uses of "se" to be very interesting.
Also this was my first encounter with "echa/echan." There does not appear to be a lesson dedicate to its conjugation, but there is this which seems to be sufficient: https://spanish.kwiziq.com/revision/grammar/expressing-instructions-and-general-statements-with-the-impersonal-se-one.
