There are a smattering of parts that we didn't cover yet so we'll introduce them now.
The little USB fuse is a part that is used to protect your Arduino and computer. You'll be connecting all sorts of wires to your Arduino and there's a chance you will accidentally short out the power. To keep your electronics safe this resettable fuse will open up, much like the circuit breakers in your home
Unlike a circuit breaker you do NOT have to switch or replace anything. Instead you just have to wait a few minutes and it will automatically heal itself
The Reset button is often right next to the USB jack but sometimes its on the right side of the board. This button is what you can use to restart the Arduino. It's handy if you want to re-run your program or if it gets stuck. It's just like restarting your phone if it hangs, but resetting an Arduino is instantaneous, it only takes about a second to restart.
This switch lets you turn on or off the DC Jack only! It is handy when powering from a wall adapter or battery pack and you want to shut off the Arduino. It does not affect the USB connection so if you power the Arduino from USB it will stay on no matter which way the switch is flipped