Okay, so you know how sometimes you play with little toys that have four different things you can do with them? Like maybe you can spin them or flip them or twist them or snap them together? That's kinda like a four-position thing.
But in grown-up world, sometimes people talk about four-position things when they're talking about something called a valve. A valve is like a little door that you can open and close to control how much stuff flows through a pipe. Maybe you've seen pipes in your house or at school or something.
So anyway, sometimes valves have four different positions you can put them in to control how much stuff flows through the pipe. Like maybe you can turn the valve one way and it lets a little bit of water through, or you can turn it another way and it lets a lot of water through, or you can turn it another way and it stops the water from going through altogether.
Four-position valves are cool because they give you more choices for how much stuff you want to flow through the pipe. It's like if your mom gave you four different kinds of juice to drink instead of just one. You can choose which one you like best!