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Question

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.

Answer

Hola William 
Just to add that the verb echar is a regular verb in all tenses (good news!) so you conjugate it following the pattern of regular -ar verbs like hablar or amar. 
You must be a bit careful with echar and hacer, because some of their forms are similar. We have a more advanced lesson and reader about this contrast, if you'd like to learn more:
Spanish words echo and hecho (lesson)
"Cotilleo" (reader using lots of expressions with echar)
: ))