A zen-tangle is sort of a recent art movement of meditation through doodling. There are several books on it, you can look it up online to learn more about it
Well, the basic idea is that you draw an approximately 5inch square and just start doodling inside it with patterns. It's "doodling with a purpose" (you're doodling but to create something beautiful The book gives you pattern ideas and such, but you can make up your own... Hope this helps and you have fun! (I learned about it from an art buddy