How is this illustration style called? How can I learn to create it?

There is a really awesome presentation on slideshare I have seen recently during a session of Powerpoint karaoke. The slides look like this:

I would like to be able to create something similar, but I have no idea how to start; I don't even know how the style is called.

How is this style called?

How is it created?

How can I learn to create images like this?