The motion displayed in the simulation does not show the full picture. If we had a real oscillator and a real force applied to it, it would move in a slightly different fashion. The mass would need a short time to "adjust" to the driving force, but after a while, it would move more and more like the long-term behavior displayed above, called the "steady-state solution".

Set the sliders so that $\omega = \omega_{0}$. Observe that the phase shift between the force and the position of the mass is exactly $90°$; the force "leads" by that amount. The amplitude of the oscillation is the greatest: for any other value of $\omega$, $\rho$ will be smaller. ($x = \rho \cdot \cos(\omega \cdot t + \theta)$)

Observe the phase shift between the force and the position of the mass. If $\omega \gt \omega_{0}$, the position lags by more than $90°$; when $\omega \lt \omega_{0}$, it lags by less than $90°$. This is visible on the plot of the force and the position too, as the two sinusoids are out of phase.