Could someone explain the steps until docking? What exactly is the fly under / first burn / second burn?
Due to the vaccuum of space, firing the rocket engines (a "burn") is required for any change in direction (the effects of gravity nonwithstanding). The burns we are looking at right now are to move the Dragon capsule closer to the ISS in the vertical dimension: First one burn to accellerate it upwards towards the ISS, and then a second burn to level it off and stop moving upwards. It will still have its _horizontal_ velocity relative to the space station after the second burn.