SER is used to explain things that you are.
Ex: Yo SOY un maestro (I'm a teacher)
ESTAR is used for actions, or conditions and also means: to be somewhere.
Ex:
- Yo ESTOY leyendo un libro. (I'm reading a book)
-Yo ESTABA cansado en ese momento. (I was tired at that moment)
-Yo ESTOY en la casa de un amigo.
HABER is used for describing things that are,were or are going to be at a period of time, the equivalent is: there+ is/are. Also used for conjugations in the past becoming the equivalent to HAVE in compound conjugations.
Hope is useful :)