Questions & Answers about Мама обычно готовит еду.
Why does the word for food end in -у (еду)?
The dictionary form of "food" is еда, which is a feminine noun ending in -а. Because the food is the direct object of the verb (the thing being cooked), it must take the Accusative case. For inanimate feminine nouns, the -а ending changes to -у, making it еду.
What if Mom was cooking soup (суп) instead? Would the ending change?
No, it would stay exactly the same: Мама обычно готовит суп. Суп is a masculine inanimate noun (it ends in a consonant). A major rule of the Accusative case is that masculine and neuter inanimate nouns do not change their endings—they look exactly like their dictionary forms!
Since Мама also ends in -а, why doesn't it change to Маму?
Мама is the subject of the sentence (the person doing the cooking), so it stays in the Nominative case (the default dictionary form). Only the direct object receiving the action changes to the Accusative case.
What is the dictionary form of the verb готовит?
The infinitive (dictionary form) is готовить (to cook or to prepare). Since мама is equivalent to "she" (она), we use the "she" form of the verb, replacing the -ить ending with -ит.