The disturbance at the top (shown in red color) is due to a source somewhere beyond the left end. The disturbance at the bottom (shown in blue color) is due to a source somewhere beyond the right end. The pattern in the middle is due to the mixing of the two.The resultant disturbance is shown in yellow color. In the middle portion a layer is shown in white color when it is at its equilibrium position. Green colored layers at the ends are for reference. They could help you to identify the intial phases of the pulses. For example the green layers are at opposite extremes of their mean positions when the pulses/waves are out of phase and on the same side extremes from their mean positions when the waves are in phase. Please watch the intial movement of these layers choosing the in/out phase alternately.