It's called Einstein Field Equation for gravitational fields.
The LHS term $G_{\mu v}$ is the Einstein Tensor
$$G_{\mu v}=R_{\mu v}+\frac{1}{2}g_{\mu v}R$$
which gives information about how the geometry of spacetime is altered by the presence of e.g. matter, pressure, energy and momentum in the universe, which are described mathematically by $T_{\mu v}$ - the Energy-Momentum Tensor on the RHS.
To be able to derive this, you need to have a rigorous mathematical background in
-Partial differential Equations
-Linear Algebra
-Tensor calculus/differential geometry.