Question

como saber cuando colocar she have //has a .i have //has a .he have //has a .she have has en útiles escolares

Answer 1

Utilizas el has solo con las terceras personas las cuales son: He/ She/ It 
+ has+ complemento.
He has a glue.
She has a pair of scissors.
It has an eraser

I have a book
we have some rulers 
you have a backpack
they have some computers

Answer 2

Respuesta:

Si es en útiles escolares u objetos debes usar IT HAS en singular o IT HASN´T en plural, porque si utilizas HE o SHE se refiere a una persona, entonces IT  se utiliza solo para objetos.