The Italian verb "essere"

The verb essere is one of the basic verbs in Italian. It can be translated as "to be".
Essere is an auxiliary verb as it helps to form Complex tenses, along with the verb avere (to have).

Here is the conjugation of the verb essere in Present tense:
io sono – I am
tu sei – you are
lui/lei/Lei è – he / she is
noi siamo – we are
voi siete – you are (2nd person plural)
loro sono – they are
The verb essere can be used:
With question words:

Chi sei? – Who are you?
Dove sei? – Where are you?
Di dove sei? – Where are you from?
Perché sei qui? – Why are you here?
Perché sei triste? – Why are you sad?
With nouns:

essere un professore – to be a professor
essere una donna / essere un uomo – to be a woman / to be a man
essere di buon umore – to be in a good mood
With adjectives:

essere felice – to be happy
essere allegro – to be cheerful
What is the difference between the verbs essere / stare?
The verb essere is used to describe general concepts, people or things.

Sono felice. – I am happy.
Sono il tuo amico. – I am your friend.
The verb stare is used to describe a state/condition, and can be translated as «to be, to feel (happy, sad etc.)», as well as «to fit/to suit, to be good (for something)».

Come stai? – Sto bene. (How are you? - I'm fine.)
Queste scarpe mi stanno bene. – These shoes fit me well.
Here are the most common set expressions with essere:
essere felice/triste – to be happy / sad
essere sano/malato – to be healthy / sick
essere libero/occupato – to be free / busy
essere sposato/sposata – to be married (sposato is for «he» (masculine), sposata is for «she» (feminine))
essere stanco – to be tired
essere pronto – to be ready
essere sicuro – to be sure
essere abituato – to be used to
essere in grado di… – to be able to…
essere in contatto con… – to be in contact with…
essere al volante – to be behind the wheel
essere di fretta – to be in a hurry
essere in tempo – to be in time
essere in ritardo – to be late
essere in coda – to be in the queue
essere a dieta – to be on a diet
essere in affitto – to be for rent (to rent a flat)
essere in debito – to be in debt
essere in possesso – to own (to be in possession)
Here are some examples of using the verb essere with modal verbs (volere, potere, dovere):
Dove può essere Anna? – Where can Anna be?
Dov'è la mia borsa? – Deve essere qui. – Where is my bag? - It must be here.
Voglio essere felice. – I want to be happy.
Non può essere vero! – It cannot be true!