Before learning how the quantum harmonic oscillator is described, you should understand the classical harmonic oscillator, reviewed here.
Consider a spring of unit force constant connecting two masses, m1 and m2. They are at rest at unit distance
separation. At time zero, they are pulled apart a fractional distance
X and released. The top figure animates their motion in time.
The red cross locates the center of mass of the system. The black crosses locate the rest positions of the masses. Mass m1 is on the left, and m2
is on the right. The green spots locate their positions at t = 0. Select values for the masses
and for X, then click the graph to animate the oscillation. Try
to predict where the center of mass will move as you change the
masses, and try to predict how the masses will move.