The verb estar (conjugation) means "to be". It is irregular in the present tense.

Estar is used to signify the location of an object:

El perro está al lado del gato. - The dog is next to the cat.
Las chicas están en la clase. - The girls are in the class.

Estar is used to express an action in progress (progressive tense):

Estoy escribiendo. - I am writing.

Estar + past participle is used to indicate a resultant condition:

Estoy cansado. - I am tired.

Estar is used to express a changeable state or condition:

María está enferma. - María is sick.
No, estamos decepcionados. - No, we are disappointed.