The English verb “to be” as translated into Spanish is ser and estar and into French is être . It is the most basic verb in English and you cannot do without it. Here is the “conjugation” of the verb:
Present tense Past tense
I am I was
You are You were
He/she/it is He/she/it was
We are we/they were
A general rule to help you to know when to use the correct form of the verb in the present tense is to memorize this maxim “singular subject, singular verb but plural subject,plural verb.”
The subject of a sentence in English describes the person, place, thing, or idea that is doing or being something. The other part of the sentence (The predicate) describes the action [what]. Hence this example: John, Mary and Catherine were in the school yard yesterday. The subject [John and Catherine] is plural the verb [were] must be plural as well.