I try to explain in short:

Quantum entanglement is simply said a physical phenomenon of instant interaction between two or more particles (photons, atoms, molekules...). Entangled particle interact instantly also if the particles are on completely different locations.

Example, if one measures the spin of +1/2 of an entangled atom that is located in X, the other atom located in Y will instantly have the spin of -1/2. Now imagine, that X is located on the Earth ond Y on Alpha Centaury, the interaction happen instantly in 0 seconds. But don't expect that one can use that for faster-than-light communication.

General relativity by Einstein simply describe the gravitation as an effect of the curvature of the spacetime. The theory says that a heavy masses like a planet, a star, a black hole etc. curve the spacetime which we feel as gravity.

As this theory is a classical field theory, it is not much compatible with the quantum theory, and this is the reason why it is so diffivult to unify this theory with quantum mechanics.

A simple example would be a black hole: it has very high gravity, the dense is infine and the volume zero. The singularity in the center of a black hole would usually described by quantum mechanichs because it is very small "point", and general theory of relativity doesn't work here. But a black hole has a macroscopic influence (the gravity, curvature of the spacetime) and can be descibed by the general relativity.

This fact makes necessary to find a way to unify the general relativity and quantum mechanics.

That's my weirdo way of explanation...