i've always been confused as though where to and not to use the concept of reduced mass...i'm not even sure if it's right to use it or not. can you please give me some clarity over it?

You can use the concept of reduced mass for only particles that are bounded by forces of mutual attraction and conditions as mentioned below.
Examples:
1.Gravitational force - Two stars bounded by the gravitational force, Earth moon system
2. Diatomic Molecule - Two atoms separated by the same distance and of course bounded by attractive forces.
In a system of masses of two of one of which is heavy(M) and other light(m), the lighter one when given a velocity moves around the heavier one in a circular orbit. However, when their masses are negligible or both masses are equal we find the centre of mass lies between them and we consider this two particle system as a single one with reduced mass( ).

Regards,

Vasantha,