The Arduino web site is the single most useful site on all Arduino information. Also, Adafruit has a ton of tutorials and educational information. For instance, I bought some tiny Arduino boards that don't even has USB on them. They are so small that they make great controllers for things that fly, or need to be small and light. On the Arduino web site I found a page that shows all the ways that the board can be programmed with a sketch. One thing I learned was that if the reset button is pressed, the boot loader will be activated, and if you connect it the way they show, program loading is simple. The other thing that I learned on that page was that you can take the processor out of an Uno board, and jumper the boards together and use the USB port from the Uno to access the other board. These boards weigh about an oz, and are no bigger than two postage stamps sitting side by side. The chip is approx 1/4" square in the center.