Peripherals are simply exterior devices you can plug into the MSP that do something when electricity is sent to a pin (which you control). They are most often plugged into the breadboard and then wires connect them to the actual MSP.
Has 4 pins. One for red, green, blue and ground. The voltage sent to the pin will affect the brightness/intensity of the corresponding color. You can create almost any color through different combinations of color intensity.
Has 16 pins. 7 of these correspond to different segments and whether they are turned on or not. 4 of these correspond to different digits and whether they are turned on or not. 1 is for the colon and the other 4 are for decimal points. To display different numbers on different digits we use a method called pulse-width-modulation (PWM).
Has 3 pins. 1 is for ground, 1 is connected to a pin on the MSP, and the other is for VCC. This peripheral will send a number back to the board that you can use to control other things (i.e. the intensity of a color in the RGB light).