The commutator in a DC Motor directs the applied DC voltage/current to the specific coil/coils such that the resultant space flux in the armature is displaced ideally 90deg with respect to the field flux, even though individual coils are rotating along with the armature, thereby ensuring the development of maximum torque. In simple words, if one coil in the armature is energized and forward torque is produced, the armature with the coil rotates. Thus, the coil position changes and it may not now be able to produce forward torque (since its position with respect to the field flux has changed) to keep the armature running. Thus, the specific coil is disconnected and another suitable coil is re-connected, all through the commutator, such that the motor is kept in rotation along with required torque generation.

It works like a bridge rectifier.

Imran, a bridge rectifier converts alternating current to unidirectional current. Since the supply is DC, sending direct current to the motor armature, how can the commutator in a DC motor "work like a bridge rectifier"? Note that current 'flows' through the armature and is not 'generated' by it in a motor. What is generated is a rotational emf and torque with mechanical power, not electrical power as in a DC generator.

The e.m.f induced in the conductors is always sinusoidal and commutator converts this sinusoidal e.m.f to unidirectional e.m.f.