Okay, here goes.
First, all matter whose temperature is above absolute zero - which is to say, ALL matter - radiates electromagnetic radiation (light). Most of the time, particularly under the conditions we have on Earth, that light is in the infrared (IR) spectrum but the actual spectrum getting radiated is determined by the temperature of the matter and is described by the Stefan-Boltzmann Equation.
The Earth is constantly chasing thermal equilibrium. At equilbrium, the amount of energy comng in to the planet from the sun would equal the amount going out via IR radiation. If the amount coming in or the amount going out change for some reason, the Earth is pushed away from equilibrium and tries to get back to it by changing the other paramters.
The path that most of that incoming energy takes is that it comes in as visible light and is either absorbed or reflected. The absorbed energy will raise the temperature of whatever absorbs it. The reflected light will either hit something else or get bounced right back to space. The energy that is absorbed raises the temperature of the gas, the ground or the oceans that absorbed it. That increased temperature will cause increased IR radiation from the stuff, which will carry that energy away. Some of that IR will hit the Earth or the seas somewhere else and get absorbed again. Some will head upwards for space. On a planet with no greenhouse gases, that energy would shoot right out to space and be gone. But greenhouse gases (GHGs) absorb IR, so the IR that the earth and the seas radiate upwards, gets absorbed by the GHGs, at the surface, almost completely within 10 meters. But, just like any other matter, that warms them up and makes them radiate more IR. So, the IR skips from CO2 molecule to water molecule to nitrous oxide molecule back to a CO2 molecule and so forth. It's direction is random so some of it gets turned around and strikes the Earth or the ocean once again and the whole thing has to start over. But some works its way higher and higher in the atmosphere.
The longer and more complex is the path that IR has to take to escape to space, the slower that energy leaves. That causes the temperature of the atmosphere, the surface of the Earth and the water in the oceans to rise.
There is a good analogy. Imagine a big tank of water that has a pipe filling it at a constant rate. That represents the sun and the energy it is constantly pouring on the Earth. The tank has a drain but there is a valve in the drain's pipe that can restrict waterflow. If that drain pipe is wide open, almost no water builds up in the tank. If we close that drain valve a bit, water will build up to some level in the tank. That level will produce enough pressure that the drain pipe and its partially open valve will let out just as much water as is coming in. But if we close the valve a little more, the water level in the tank will rise. This is like heat and CO2. Added CO2 slows the escape of IR and the planet will warm until it is pushing IR out hard enough that it once again equals the incoming solar energy. Raise the CO2 level and the temperature will go up again.
I know this is a pretty crappy explanation. I should have been able to do better but I've been doing some projects at the same time and did this sort of piecemeal, hit-or-miss. Sorry. The internet is full of people explaining how it works, better than this. Give them a shot. Point is, global warming does not require extra energy input. It's just like you warming yourself up at night by getting under a blanket.
