Question

Why were you able to see the effects of the magnetic fields using iron filings

Answer 1

The iron filings aligned themselves in a pattern, along with the magnet connecting the north and south poles. This creates the “magnetic field”. Interacting with a metal object in between the magnetic properties of the metal interact with the magnet, expressing signs of magnetic force acting on it and the metal, pulled together letting you see the see the effects of the magnetic fields using iron filings. 

Answer 2

Iron filing are soft magnetic materials. The are highly attracted by magnets. 
They are used in the study of magnetic fields.
Another reason why they are used because they are light and and they can aline themselves in the paths of the magnetic fields. This way the fields patterns can be seen clearly.