Spacetime metrics are mathematical tools used in physics to describe the structure of spacetime, which combines the three dimensions of space with the dimension of time. These metrics help determine how distances and times are measured in the presence of gravity, as described by Albert Einstein's theory of general relativity. In essence, a spacetime metric provides a way to calculate the interval between two events in spacetime, taking into account the curvature caused by mass and energy. Different metrics, such as the Minkowski metric for flat spacetime or the Schwarzschild metric for a spherical mass, illustrate how gravity influences the geometry of the universe.