1. Elle va à l'école. (This is the most common and general way to say it)
* Elle: She
* va: goes (verb "aller" in the present tense, 3rd person singular)
* à: to
* l'école: school (feminine noun, so "l'" before the word)
2. Elle est à l'école. (This means she is at school, implying she is currently there)
* Elle: She
* est: is (verb "être" in the present tense, 3rd person singular)
* à: at
* l'école: school