THE VERB "FICAR" :

The verb "ficar" can be used as an alternative to "ser" when expressing permanent location:

Porto Alegre fica no sul do Brasil.

Porto Alegre is in the south of Brazil.

Before an adjective, "ficar" marks a transition to a new state, usually as a reaction to something else. It often translates ‘to get, become’, but should be used to translate ‘to be’

when a change of emotional state is implied:

Fiquei contente em saber que você está bem.

I was glad to hear that you are well. (i.e. I became glad when I heard)

Não fique triste.

Don’t be sad. (i.e. Don’t get sad)

Like estar, ficar can only be followed by a noun used metaphorically to describe a new
state:
Meu cabelo vai ficar um lixo com essa chuva.
My hair’s going to be a right mess with this rain.

Also, ficar can be followed by a past participle to express an involuntary passive result
Ficamos presos no elevador.
We got stuck in the lift.

ref.: Modern Brazilian Portuguese Grammar - A Practical Guide.