The space shuttle solid rocket booster is like a really big fireworks rocket that helps the space shuttle launch into space. The rocket booster is made up of two big tubes that are attached together at the bottom. These tubes are filled with a special fuel called solid propellant, which is like a really powerful explosive. When the space shuttle is ready to launch, the solid rocket boosters are ignited and start burning the solid propellant, making a lot of hot gas that shoots out from the bottom of the tubes.
The hot gas shoots out with a lot of force, pushing the space shuttle off the launch pad and into the air. The rocket boosters burn for about two minutes, giving the space shuttle the extra power it needs to escape Earth's gravity and get into space. After the boosters burn out, they separate and fall back to Earth, where they are recovered and used again for the next space mission.
So, imagine you want to launch something really, really big into the sky, and you need a lot of power to do it. That's what the space shuttle solid rocket booster is for - it's like a giant firework that gives the space shuttle the extra oomph it needs to fly up to space!