How do you make a sound thing to put into a stuffed animal?

I don't know the technical term, so I'm using layman's terms. I've been getting into making my own stuffed animals, and now I'd like to know how to put sounds into them. You know, when you squeeze a hand or something, and it says something or makes a noise? How do you make those? Any website to tell me/teach me, or maybe a diagram of how to make the device, then to add the sound? I'm not really technical, so keep it in layman's terms, please.