This is the 94th most frequent Spanish word.
estar
"Estar" means "to be" and is used to indicate temporary states, locations, or conditions.
Here, 'estar' indicates location, describing where the subject is at the moment.
Estoy en la escuela.
I am at school.
In this sentence, 'estar' expresses a temporary state or emotional condition of the subject.
Estoy feliz hoy.
I am happy today.
This instance of 'estar' describes a temporary state or condition of an object.