What can computer do?

What /can't/ a computer do? In theory, computers can do any "computation" which is a fancy way of saying they can take numerical input, perform mathematical operations on them, and then return numerical output. Of course, people don't like numerical input and output, so we've invented fancy ways to encode things like text and pictures into numbers, so we can have our computers do stuff like spell check and send things over the internet. Most people use computers for Word processing (typing and editing stuff), Surfing the internet (getting articles and pictures from other people's computers), and playing games.