The pinout diagrams are simple, but they're easy to read, and especially helpful for beginners. You can print them out full size so you can set your Arduino Uno, ATMega, or ATTiny right on top for ...

The Arduino Nano and Uno are equipped with very similar processors (the chip that essentially serves as the brain of the board). The Nano features an ATmega328, while the Uno sports an ATmega328P.