In a nutshell, what is single side band?
I looked Wikipedia article on topic, right, I wouldn't get that either, if it was the only source.
In nutshell: using SSB makes possible to separate two different transmissions in the frequency space that one AM signal uses. AM uses both sidebands, SSB only lower or upper, that's why it's called single.
What one need to know: broadcast radio uses AM. Shortwave Maritime radio, air volmets and radio amateurs use ssb. Under 10 MHz amateurs use LSB, over 10 MHz USB. From the point of view of listener this information is enough to select a right button.
Decades ago (sorry...) there were experiments by Radio Sweden and HCJB among others to transmit programmes on SSB, but it never became popular as average portables of the time didn't have ssb feature.