Dear Student,
If the function of the displacement of the particle x(t) is known to us, then instantaneous velocity can be calculated by differentiating the displacement function at any given time at which we are interested to calculate the instantaneous velocity.
If the function of the velocity of the particle v(t) is known to us, then instantaneous acceleration can be calculated by differentiating the velocity function at any given time at which we are interested to calculate the instantaneous acceleration.
Regards,