Answers:
The spanish (castillian) Preterite Tense is a form of the Simple Past Tense, which is used to express specific actions completed or concluded in the past that are separated from the present.
In other words:
It is applied when the person speaking gives information about the past that is not related to the present.
Knowing this, let's answer the questions:
1. Juan / pedir / un bistec / en el restaurante.
The verb pedir (to order) conjugated in preterite with the 3rd person in singular Juan (he) is pidió (he ordered).
Juan pidió un bistec en el restaurante.
Juan ordered a steak at the restaurant.
2. (nosotros) / preferir / este restaurante al restaurante italiano
The verb preferir (to prefer) conjugated in preterite with the 1st person in plural nosotros (we) is preferimos (we preferred).
(nosotros) Preferimos este restaurante al restaurante italiano
We preferred this restaurant to the Italian restaurant
3. mis amigos / seguir / a Gustavo para encontrar el restaurante
The verb seguir (to follow) conjugated in preterite with the 3rd person in plural ellos (they), which are "mis amigos" is siguieron (they followed).
Mis amigos siguieron a Gustavo para encontrar el restaurante
My friends followed Gustavo to find the restaurant
4. la camarera / servirte / huevos fritos y café con leche
The verb servir (to serve) conjugated in preterite with the 3rd person in singular ella (she) which is "la camarera" is sirvió (she served).
La camarera te sirvió huevos fritos y café con leche
The waitress served you fried eggs and coffee with milk
5. ustedes / pedir / ensalada de mariscos y vino blanco
The verb pedir (to order) conjugated in preterite with the 2nd person in plural ustedes (you) is pidieron (you ordered).
Ustedes pidieron ensalada de mariscos y vino blanco
You ordered seafood salad and white wine
6. Carlos / preferir / las papas fritas
The verb preferir (to prefer) conjugated in preterite with the 3rd person in singular él (he) which is "Carlos" is prefirió (he preferred).
Carlos prefirió las papas fritas
Carlos preferred French fries
7. (yo) / conseguir / el menú del restaurante
The verb conseguir (to get) conjugated in preterite with the 1st person in singular yo (I) is conseguí (I got).
(yo) Conseguí el menú del restaurante
I got the restaurant menu