I was going to write up a tutorial here, but there's already an excellent one on Cake Central!
If you want something that dries quicker and is already prepared for you, check out Wilton.
Wilton fondant can also be purchased at many hobby shops and cake decorator supply stores.
Follow this link for product information on Wilton Fondant, including how to color, store, helpful tips, and techniques.
Gum Paste Tools
The gum paste tools I use to make Thomas' face can also be found at many hobby shops and cake decorator supply stores. You may also buy it online at Wilton.