If you arrive by plain in the Guarulhos Airport, you need take the CPTM train line and go to Tatuapé. Then you change to the red line and go to Sé subway station. After, you take the blue line and go to Praça da Árvore station. You need to walk ten minutes to arrive in Hostel Casa Azul.
If you arrive by plain in the Congonhas Airport, the best way is take a uber or a taxi. It is very cheap.