Here's a video to showcase unit conversion in action.
Okay, now how do you use all this newfound knowledge to do something practical? There are a bazillion ways (estimated) to use formulas, but one common one is unit conversion, the converting of a number to an equivalent value that's expressed in different terms. This can mean translating a temperature in Celsius to Fahrenheit, translating U.S. dollars to yen, or translating any one of our silly American systems of measurement over to the far superior metric system. Boy oh boy, if only we could get our hands on the wise guy who invented the foot...
If you'd like to see a huge list of conversion formulas, including conversions between units you've probably never even heard of, check this out.
For our purposes, however, we'll go through a much smaller selection of conversion formulas having to do with temperature, weight, distance, speed, and money.