In order to save space and increase flexibility for projects the ExtraCore doesn't have an on board power regulator. That means you have to provide 5v exactly to the power pin. Lots of Ardunio projects can run off a 9v battery to the RAW pin. The ExtraCore is lacking a raw pin, but you can make your own with the bonus parts.
You have a power regulator and two capacitors as a bonus with each built board. The power regulator is very flexible with a lot of features. Luckily it's also really easy to use.
You can find the datasheet here: http://www.infineon.com/dgdl/IFX25001_DS_101.pdf?folderId=db3a30431ff988150120802bce1d257a&fileId=db3a304320d39d590120f620f1e269da
If you put it face down on the table, raw power goes in the left most pin. The center pin is ground, and pure, clean 5.0 volts comes out the right pin. Two external capacitors are provided for best results. One goes from the input to ground, the other goes from output to ground. The capacitors are color coded and the strip goes to ground. Add them as close as you can to the power regulator in your circuit.
Now the RAW pin can take voltages from 5.5v all the way to 40v! If you provide more than 12v you may need an external heat sync to attach to the power regulator. Most 5v wall adapters actually put out 5.5-6.0 volts that is ready for use as input.