To be = être

Have a look at the conjugation of this verb with audio here: être

1. To be + Adjective

There is an agreement between the subject and the adjective:
Masculine: il est blanc
Feminine: elle est blanche

M: Ils sont grands
F: Elles sont grandes

M: Tu es français (no capital letter for adjectives)
F: Tu es française

An adjective that has a masculine form ending with an -e does not change:
M: Il est tranquille
F: elle est tranquille

Pay attention with the color adjectives, the rule for plural may be different: Color

2. To be + profession

There is no indefinite article:
I am a doctor: Je suis docteur
She is a student: Elle est étudiante

3. C’est: it is, he is, she is

We use “c’est” + nouns:
He is a friend: the noun is ‘friend’ so we translate ‘he is’ with “c’est”  C’est un ami ( and not: il est un ami)
She is a friend of mine: c’est une de mes amies.

We also use “c’est” with adjectives when we speak generally:
Les fleurs, c’est beau (beau does not agree with fleurs which is feminine but with c’), when you describe something, you can use “c’est”.
Ces fleurs, elles sont belles (here we are speaking specifically about ‘these flowers’)
Où est Paris? c’est en France (here no problem, Paris is not a person)

When we refer to someone specifically we use the proper pronoun (and also with professions): il, elle
Pierre? il est docteur, c’est un très bon docteur (the adjective “bon” requires “c’est”,  so we don’t say: il est un très bon docteur)
Pierre, il est grand (specifically)

We like to use “c’est” to insist:
Mon frère est en train de chanter  C’est mon frère qui chante! (my brother is singing)

More about C’est vs Il: Lesson

4. More

Être is also one of the two auxiliary verbs we use with past participles.