It's a verb, so it changes its form depending on the context.
Here are some examples:
* Yo estudio español. (I study Spanish.)
* Ellos estudian matemáticas. (They study math.)
* Ella estudió mucho para el examen. (She studied a lot for the exam.)
* ¿Estás estudiando para el examen? (Are you studying for the exam?)
It's important to note that "estudian" is the third person plural form of the verb "estudiar."