yourpi:~$ wget https://project-downloads.drogon.net/wiringpi-latest.deb

NOTE: domain say “dr-OH-gon”, it does NOT say “dragon”

yourpi:~$ sudo dpkg -i wiringpi-latest.deb

“gpio readall” will open up a table showing the physical pin layout of your pi. It will also tell you whether a pin is set to input or output, and whether the pin is turned on or off (V=0 shows the pin is off, v=1 shows the pin is on).

“gpio mode WIRINGPI_PIN# MODE” will change the mode of the designated pin. You must use the WiringPi pin number. Mode can either be in (input) or out (output).

“gpio write WIRINGPI_PIN# STATE” will change the ON/OFF state of a pin. 0=off and 1=on

The ground “pin” is extremely important if connecting a circuit together. If done without a ground you can easily fry your breadboard or even kill an L.E.D light. Your ground pins are indicated by a GND next to the designated pin. For every power source connection, you must have a ground wire going to one of the Negative column.

GPIO.0 is actually GPIO17 on your T-cobbler

Brief Definition:

A light-emitting diode (LED) is a semiconductor device that emits light
when current flows through it.

Light-emitting diodes only allow electrical current to pass through them one way. The longer lead is the positive connection, and the shorter lead is the negative connection.