The Raspberry Pi has 26 GPIO pins. What are the names, functions, and important limitations of each?
The GPIO pins can be used as digital inputs or outputs. Additionally some of them can have alternative purpose like UART or I2C. Afaik the naming is from GPIO 0 to 31. Some of the GPIO pins can not be found on connector P1 and serve different purposes like switching onboard LED (GPIO 16) or HDMI Hotplug (GPIO 46). These can normally not be used for other things. Other GPIO pins can be found on different connectors e.g. P5 (GPIO 28-31).
To make working with the GPIO pins easier, check out PiCrust. http://picru.st/ Its an open source add-on board which breaks out the pins in an organised sense. The site links to a page where you can order it, and it comes to about $14 for 3, plus the headers that would need to be soldered on by you. Makes the pi more friendly to newbs like us I'd say.