Any good links to lecture notes or anyone can explain the underlying concepts here? Are we just dealing with a summation of points constituting a single object? I am sorry if this question is too general or broad. Maybe a more specific question is why there are 6 coordinates needed to describe such multiparticle systems where we are dealing with 3+ particles.
Ed Quanta, The term "rigid body" refers to a system with any number of particles, but which are constrained not to move relative to eachother. That is, a rigid body does not deform. However, a net force applied at some point on the body will cause it to accelerate, and that acceleration will be in some direction defined by the 3 coordiantes: x, y, and z. And if the center of mass of the body is not on the line defined by the force's direction and the point where it's applied, the body will be angularly accelerated around an axis defined by the 3 angles it makes to x, y and z. That makes 6 coordinates needed to describe the motion of a rigid body.