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

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

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

Voltage is the difference in electrical potential. In ohmic materials, V=IR, or voltage is equal to the product of the electric current times resistance. 1 volt equals 1 joule per coulomb.

An LED is actually just an acronym for “Light Emitting Device”.