Below is the official TouchDesigner Introductory video. There are Wiki entries for both of these videos, containing the transcript, useful links, and an ability for you to more slowly read and follow along.
I am including these videos, as they are the official suggestion from Derivative on how to get started.
{ NOTE: } You can choose to follow along to the videos on this page or not. I will walk you through a “Hello World” later in this weeks content.
Part 1
Part 2