Think of it kind of like FM Radio. FM broadcasts between 87.9 and 107.9 and in between you have different channels.
So, to make the comparison: think of your 2.4ghz network as FM radio, in general. And then, you have a number of channels/frequencies within that can be broadcast. In the US, it’s usually channels 1-11.
It’s just a much smaller scale. With lots of people broadcasting radio stations in a smaller area, but the signals don’t travel as far.
Then, have you ever seen where you tune into say 92.5, but it’s kind of weak signal, but another station sometimes comes through over it? That station could be on the exact same 92.5, or even 92.3 or 92.7. You only hear one station at a time though - not both at once.
Equating that to 2.4ghz - if your router is broadcasting/talking on channel 6… Tom is on channel 9, and Julesmakesthings is on channel 11… your channel 6 actually utilizes frequencies that range between say channel 4 and channel 8. So you and Julesmakesthings wouldn’t have any crosstalk. Tom is on channel nine, and utilizing frequencies between channels 7 and 11. So he is crosstalking with both you and Julesmakesthings. And finally Julesmakesthings on channel 11, is clear of your radio station, but is getting crosstalk with Tom.
This makes tom sound like the bad guy, when he may not necessarily be. It’s just an example. Everyone around tom could have been on channels 1-6 at some point, and his channel 9 was relatively clear. And that could also change, since many routers are set up to automatically change the radio station. They could have said, dang, it’s crowded down here, let’s change to channel 11. And now Tom, who was free and clear, is sharing radiowaves and radio bandwidth with other people.