There are pins for Serial/UART communication, and a pin for resetting your device. There are also pins to allow you to power your device, or power motors and outputs outside of your device. GPIO pins can be hooked to sensors or buttons to listen to the world, or they can be hooked to lights and buzzers to act upon the world. Pins are the input and output parts of the microcontroller that are exposed on the sides of your device.

The microcontroller interacts with the outside world using pins.

This application can be simple (just a few lines of code), or very complex, depending on what you want to do. Unlike your computer, it can only run one application (often called firmware or an embedded application). It runs your software and tells your prototype what to do. The microcontroller is the brain of your device. Doing so triggers a reset and is generally not good for the Photon. Do not press down on the Photon's module. It connects your device to the internet in the same way that your smartphone might connect to a wifi network. This is probably why you bought your device- the Wi-Fi module allows your Photon to communicate with the internet.

Set up your Photon What's on it? The Wi-Fi module

Photon modem driver download