You're asking about stealth, but lets describe it easy.

Think about radar cross section like this: I put on a blind fold and I throw a ball forward. If it hits anything, it bounces back, so I know there is at least something there. If I throw it and it doesn't come back, I can assume there is nothing there. thats how radar works, but with radio waves, not a ball.

The radar cross section, is basically like if there was a moving target when I throw the ball. Except instead of one ball, I throw like a hundred. With a hundred balls, I can hit it easily if its big, but lets say its super tiny, like the size of a bee, its gonna be way hard to hit, so I may never even know its there.

Ok, but even those hundred balls, eventually I will know its there, say 1 in every 1000 balls hits it but its gonna be really hard to figure out where its going and whats happening when only 1/1000 balls hit it.

Radar bounces a signal off flying things and then reads the blip caused by it. Normal planes show up as large blips, they reflect a lot. Stealth aircraft use materials and angles to reduce what goes back to the radar making it look smaller. Like the f22 apparently looks like a small bird so most radar technitions won't notice that since there are many small things.

It's the apparent size something appears to be based on how much radar signal it bounces back.
So a stealth bomber with a radar cross section of 10 square feet bounces back as much radar signal as a non-stealth blunt object with a surface size of 10 square feet facing the radar station. So it appears as a tiny object on the radar, if it appears at all, despite actually being big.

Radio waves bounce off stuff. Radars send out radio waves, then measure how much bounces back, and from where. Stealth lets an airplane redirect or absorb most of these radio waves so what bounces back resembles something more like a goose than a fighter jet.

There are two types of radar: Primary and secondary. Secondary radar works by detecting an aircraft's transmitter and doesn't apply here, but primary works by sending radio waves from a ground station and then monitoring for signals that are returned to the ground station -- reflections -- to make a determination about an aircraft's speed and bearing. The radar cross-section of an aircraft is a measure of how susceptible it is to detection by primary radar from different angles.

Radar works by transmitting and observing the reflections of radio waves. Which are electromagnetic waves not unlike visible light, except in a different frequency, so we can use a visible light metaphor.

Imagine you are in the middle of a vast open field, and it's the middle of the night: there is no ambient light. But you have been equipped with a powerful flashlight, which you can point in any direction you like. You are also equipped with a partner we'll call Sam. Sam will go where you point if you command him to, and he's a very fast runner, but it takes him a few second

There are five enemies out there. Their job is to tag you out, but they lose if Sam tags them first.

Assassin 1 is vastly obese and is wearing a cheap white shirt. You spot him easily and Sam tags him out: he has an immense cross section.

Assassin 2 is just as obese but is wearing all black. Your flashlight does not reflect off him as well, but as he is such a large and slow moving target you have no problem seeing him in time to send Sam after him. His physical cross section is the same but his visual cross section is far less.

Assassin 3 is very athletic- not as fast as Sam, but damn fast. Still didn't pay attention to his wardrobe, though: his white shirt gives him more than enough cross section for you to see him and Sam to run him down before he reaches you.

Assassin 4 is like 3 but wearing all black. You barely spot him in time.

Assassin 5 came prepared. He spent a lot of time, money, and effort to camouflage himself. He can't change his physical cross section, but visually, you can't detect him because none of the light from your flashlight is returning to the detector-your eyes- in a way you recognize as a meaningful object.

It works exactly like you looking around a room. Large objects take up more space in your vision so it's easier to see. Smaller objects are harder to spot. Transparent objects are even harder to see.

Radar works like your eyes, except you can't really see the details of the object. Just how big it is, like you are really near sided and everything is just blurry shapes in the distance. With stealth, they shape the object to make it mostly transparent to radar, like a glass window for visible light. They also use radar absorbent materials, which is like painting an object black to hide it in a dark room. Both of these reduce the radar cross section.

Radar cross section could be used to approximate what a jet would look like on radar relevant to other things and basically describes how easy it is to spot on radar.

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