Questions & Answers about Marinamos el solomillo hoy.
Marinamos tells you the subject is we.
It is the first-person plural form of marinar in the indicative. So the sentence is built around we marinate / we are marinating / we marinated, depending on context.
Because the verb ending already shows we, Spanish usually does not need the subject pronoun nosotros.
Spanish often drops subject pronouns because the verb ending already makes the subject clear.
- Marinamos = we marinate
- Marino = I marinate
- Marinan = they / you all marinate
So Marinamos el solomillo hoy is perfectly natural without nosotros.
You could say Nosotros marinamos el solomillo hoy, but that adds emphasis, as if you were contrasting we with someone else.