In Einstein's theory, gravity is not a force but a curvature of spacetime caused by mass. Massive objects bend the fabric of spacetime, altering the path of light and the flow of time.
The grid represents spacetime, which warps in the presence of mass. Light follows the curved paths (geodesics) of spacetime, demonstrating gravitational lensing.
Time also flows differently in regions of higher gravity - a phenomenon called gravitational time dilation. The clock near massive objects runs slower than clocks farther away.