• PARA + SUSTANTIVO O PRONOMBRE: FOR
This is for Mary.   
(Esto es para Mary.)
I've bought it for my brother.  
(Lo he comprado para mi hermano.)

• PARA + VERBO:
FOR + verbo en -ing   (finalidad de un objeto).
This switch is for starting the engine.
(Este botón es para arrancar el motor.)

TO / IN ORDER TO / SO AS TO + verbo en infinitivo
He came to speak.
He came in order to / so as to speak.
(Él vino para hablar.)

Pero ante un infinitivo negativo: SO AS NOT TO / IN ORDER NOT TO
He left so as not to / in order not to meet them.
(He left not to meet them.)
(Se marchó para no encontrarse con ellos.)

• PARA + ORACIÓN:
SO THAT / IN ORDER THAT + can / could / will / would
He gave me the key so that / in order that I could open the door.
(Me dio la llave para que pudiera abrir la puerta.)