Okay, kiddo, let me try to explain prestressed structure in a way you can understand.
Have you ever played with a rubber band before? When you stretch it, it gets longer and thinner, but when you let it go, it springs back to its original shape. This is kind of like what happens with a prestressed structure.
A prestressed structure is a type of building or bridge that is made stronger by putting stress, or tension, into certain parts of it before it is even used. This stress is usually applied by steel wires or cables that are tightened up really tight - kind of like stretching a rubber band really far.
When the structure is then used, the stress helps it to withstand heavy loads, like lots of people or cars crossing over a bridge. Without this stress, the structure might not be strong enough and it could collapse or fall apart.
So, the next time you see a big bridge or building, remember that it might be a prestressed structure, and that means it's strong like a rubber band!