Note that the mean energy of the particles does not change. However, since the frequency of collisions increases (they happen more often), the frequency of successful collisions also increases.
The gradient of the line is equal to the rate of reaction. The faster reaction at the higher concentration or pressure:
Note that the amount of product does not change when the reaction rate changes. The same amount of product is formed, but in a shorter time. Therefore, both lines on the graph finish in the same value of mass or volume, but the reaction at the higher concentration or pressure reaches this mass or volume sooner.