Questions & Answers about Мы заказали пиццу.
Because пицца is the direct object of the verb заказали (ordered), so it goes into the accusative case.
- Dictionary form: пицца
- Accusative singular: пиццу
This is very common in Russian: the thing receiving the action often changes form.
Compare:
- У нас есть пицца. = We have pizza.
- Мы заказали пиццу. = We ordered pizza.
Because the subject is мы (we), and in the past tense Russian verbs agree in number.
Past tense forms of заказать:
- заказал = he ordered
- заказала = she ordered
- заказало = it ordered
- заказали = they ordered / we ordered / you all ordered
So заказали is the plural past tense form.