Okay, imagine you are watching a cartoon on TV, but you want to flip back and forth between the different channels to see which show you like the best.
An all-channel receiver is like a big machine that helps you do this. It can tune in to all of the different channels that your TV can get, so you can switch from one channel to another with just a push of a button.
Think of it like having a magic wand that can change the channel for you without having to get up off the couch.
All-channel receivers are really handy for people who like to watch a lot of TV, because they make it easy to switch from one show to another without having to do a lot of work.