One of the great things about the Raspberry Pi is that it has a GPIO connector to which you can attach external hardware.
The GPIO connector actually has a number of different types of connection on them. There are:
True GPIO (General Purpose Input Output) pins that you can use to turn LEDs on and off etc.
I2C interface pins that allow you to connect hardware modules with just two control pins
SPI interface with SPI devices, a similar concept to I2C but a different standard
Serial Rx and Tx pins for communication with serial peripherals
In addition, some of the pins can be used for PWM (pulse Width Modulation) for power control and another type of pulse generation for controlling servo motors called PPM (Pulse Position Modulation).
In this tutorial, you are not actually build anything, but you will learn how to configure your Raspberry Pi and install useful libraries ready to start attaching some external electronics to it.