wow... good question. Not a simple answer.
Be can be translated into 2 different verbs that are NOT exchangeable: SER o ESTAR.
They're used differently:
SER is used to express identification (followed by a noun. Ella es una modelo = she's a model); description is normally followed by adjectives that don't derive from verbs in past participle (the apple is red = La manzana es roja; La pintura es hermosa = the painting is beautiful) ; and passive voice (Mi coche fue fabricado en Alemania = My car was manufactured in Germany)
With the exception of the passive voice, we could say that SER is the verb to BE
ESTAR: expresses a temporary state of being, or a state of being that wasn't present hitherto (for example: he's dead , although it's a description, it is incorrect to say: él es muerto. The correct way is: El está muerto; because he wasn't dead before). A continuous tense (Estoy escribiendo = I'm typing). Description with an adjective derived from a past participle (La ventana está rota = The window is broken)
In this case Estar could be the Auxiliary to Be. Although, for passive voice, in spanish you should use the verb to be, rather than the auxiliary to be.
Grasping the difference between the 2 can be a little tricky.
El carro es pintado (the car is painted, as a process. In this case a time expression or an adverb of place would make the sentence more meaningful) El carro es entonces pintado en el area de pintado (the car is then painted in the painting area).
El carro está pintado en rojo (the car is painted red).
Hope this was helpful