This breakout board is designed to make it easy for you to get started with the Atmega32u4, a USB-native 8 bit AVR microcontroller. We tried to keep the design simple, while taking care of all the details so that you can focus on your project's firmware and hardware.
The main chip is an ATmega32u4, an 8 bit AVR-core processor which has the bonus of a USB core built in. This makes writing USB native programs such as serial ports, mouse/keyboard, mass-storage-controller, MIDI, etc very easy. The chip has 32K of flash and 2.5K of RAM. The microcontroller is clocked at 16 MHz with an on-board crystal.
The board is powered by the USB port at 5V. There is a 500mA polyfuse to protect your computer from a shorted circuit. If you'd like to run the board off of another voltage, you can do that by cutting the VCC solder jumper bridge underneath and connecting an external voltage to pin #2 of the ISP header. Note that running the board at 3.3v @16mhz is considered overclocking. We do it for prototypes and it seems to work fine but it's out of spec!
There is a 3V pin from the microcontroller's internal regulator (USB signals are at 3V) you can use this for maybe 10mA or so, it might work as a reference voltage).
Pins are labeled on the silkscreen, but for additional information, Johngineer has created a nice pinout diagram that is helpful for using this board.
The very nice thing about this chip is the USB core built in which makes USB-device development easy. What makes it even easier & better is the full USB stack already written for you by Dean Camera . Called "LUFA" , the package comes with tons of working examples for all sorts of USB devices and its completely open source. We use the firmware as a 'starting point' which we then expand upon. Please check it out and if you find it useful consider donating time (fixing bugs, improving documentation) or funds to Dean.