Do you know how a typewriter works? It has a big black ribbon with letters on it, and when you press a key, a metal arm with a letter on the end hits the ribbon and makes a letter appear on the paper.
A typeball printer is kind of like a really fancy typewriter. Instead of a metal arm with one letter on the end, the printer has a ball-shaped thing with all the letters, numbers, and symbols on it. The ball spins around so the right letter can be hit onto the paper.
The typeball is really cool because you can change it really easily, just by popping one off and putting another one on. This means you can use different fonts and languages without having to buy a whole new printer.
Some people still use typeball printers today, but most people use digital printers or computers to make words appear on paper.