Kinematics are the way that kinematic energy (velocities) is distributed among stars in a sample. The average velocity of stars and the dispersion of velocities in a sample tell us about the motion of this sample as well as their spatial distribution if placed in a gravitational potential. So the average velocity of stars in the disk of the galaxy tell us how fast it is rotating and since the disk of the galaxy has a gravitational potential, we can calculate how far the disk stars are spread from the galactic plane by their velocity dispersion perpendicular to the plane of the galaxy.