Could prepare be considered as a translation for robić or it's not the precise meaning?
Prepare is przygotowywać. Generally, robić can replace a lot of different verbs. It's very common.
robić literally translates as "to make" in English. You can use it in many of the same contexts as the English verb.
It told me that "My mama makes tasty sandwiches" is a wrong translation. Why?
"Mama" is a very good word in English. The word is even in songs like: "My mama told me not to come" by the Three Dog Night and "Mama Mia" by Abba. Does it mean something different in Polish? Please explain!
English clearly doesn't want to decide how to call one's mother ;) So many variants that people want... ok, added "mama".
The main English answer is always either "mom" or "mother". I changed "mother" to "mom" now, but "mom" was accepted. It actually is automatically accepted if only "mother" is. And the other way round.