First simple model - earth climate

The earth is a ball of iron alloy, coated in rock, coated mostly in water, with a gas layer on top.
Heat (energy) comes out from the center to the rock/gas and water/gas interfaces, where we live.
Energy comes in through space from the sun.
Energy is radiated from the outside of the earth, from the interfaces out to the outside of the gas layer, into space.

The earth does not put out enough energy to keep the surface from freezing without help from the sun.
This is the basic energy-flow model.