Imagine you have a toy that makes sound by shaking it. Sometimes when you shake it really hard, it doesn't just make one sound, but also some extra little noises that you hear at the same time. These extra noises are called "sidebands".
In electronics, we use a similar idea. When we send out a signal, like music or a radio wave, it can sometimes have extra little signals on either side of the main one. These are also called sidebands. They happen because of the way the signal travels through the air or wires.
If you're listening to the radio and there's a lot of static or hissing, that might be caused by sidebands. They can also be really useful in things like radar or other communication systems, because they let us send more information along the same signal.
So, think of sidebands like the little extra sounds you might hear when you shake a toy. They're not always there, but when they are, they can add more interest and information to the main signal.