Commutator :  

       The function of commutator is to facillitate collection of current from the armature conductors. It also rectifies i.e. converts alternating current (ac) to direct current(dc). It is made up of high conductivity hard-drawn or drop-forged copper.

Brush :

       The function of brush is to collect current from commutator. They are usually made of  carbon since carbon is a good conductor and produces less friction than metals.

Fleming's Left-Hand Rule