The verb ser (conjugation) means "to be". It is completely irregular in the present tense.
||you guys are
||you all/they are
Ser is used to signify equivalence or identity between two elements:
Mi esposa es doctora. - My wife is a doctor.
Ser is used to indicate an inherent characteristic or quality:
El niño es guapo. - The boy is handsome.
Ser is used to indicate origin:
Yo soy de Colombia. - I'm from Colombia.
Ser is used to express ownership or possession:
Ese carro, el cual está muy sucio, es de Enrique.
That car, that is very dirty, is Enrique's.
Ser is used to express the time of day:
Son las doce. - It's twelve o'clock.
Ser is used to talk about dates
Es el primero de enero. - It is the first of January.
The verb estar (conjugation) means "to be". It is irregular in the present tense.
||(you guys are)
||(you all/they are)
Estar is used to signify the location of an object:
El perro está al lado del gato.
The dog is next to the cat.
Estar + past participle is used to indicate a resultant condition:
I am tired.
Estar is used to express a changeable state or condition:
María está enferma.
María is sick.
Ser is used as a true auxiliary, when it forms the passive voice.
Estar is an auxiliary when it forms the progressive tenses, as:
Estoy escribiendo (I am writing).
Estaba escribiendo (he was writing).
The difficulty in the employment of ser and estar is, by some, unduly magnified. Others give the following rule:
Ser denotes a permanent state.
Estar denotes a temporary state.
This rule should not be adopted because often it would not apply, as the following two Examples will show:
Él es soldado porque se ha alistado por dos años.
He is a soldier as he has enlisted for two years.
Aquellos montes están eternamente cubiertos de nieve.
Those mountains are perpetually covered with snow.
The following simple and true rules will enable the student to understand the difference between ser and estar and to apply them correctly.
Ser is used:
1. To form the Passive Voice, as:
El cartero trajo las cartas--Active: The postman brought the letters.
La carta fué traída por el cartero--Passive: The letter was brought by the postman.
Footnote 1: The Past Part. following "Ser" and "Estar" agrees in gender and number with the subject of these verbs.
Footnote 2: Este cuarto es barrido todos los días (this room is swept every day) is passive voice, because we speak of the action of sweeping, viz., somebody sweeps the room every day. Este cuarto está barrido--no voice; "barrido" is used as an adjective to denote state or condition.
2. To denote an inherent quality, as:
La nieve es blanca: Snow is white.
El hombre es mortal: Man is mortal.
Footnote 3: Inherence = a fixed state of being in another body. A quality may be inherent "for the time being," as: Juan se ha alistado por dos años, entonces es soldado: John has enlisted for two years, then he is a soldier.
Estar is used to denote:
1. State in locality, viz., to be in a place, as:
I am here.
Londres está en Inglaterra.
London is in England.
2. A condition, as:
I am tired.
He is ill.
Ser must be used--
1. Before any noun (even if an adjective or article intervenes), as:
I am a merchant.
Es un corredor de cambios bien conocido.
He is a well-known exchange broker.
Son buenos valores.
They are good securities.
2. When "to be" is used to denote possession, as:
Los trapiches son de estos fabricantes.
The sugar mills belong to these makers.
3. When "to be" us used impersonally, as:
Es necesario tomar medidas legales.
It is necessary to take legal proceedings.
4. Before the words "Feliz," "Infeliz," "Pobre," and "Rico." 
Footnote 4: These are not, strictly speaking, "inherent qualities," but they are spoken of as such.
Estar must, of course, be always used before Present Participles, 
Está activando sus esfuerzos.
He is making still further efforts.
Estamos extendiendo nuestras relaciones.
We are extending our connection.
Footnote 5: A Pres. Part. can only express a condition, not a quality.