Fuels

There are three main fuels that you need to be familiar with:

Coal has been formed by the anaerobic decay of vegetation over millions of years. Anaerobic means in the absence of oxygen
Natural gas is mainly methane
Petroleum (or crude oil) is a complex mixture of hydrocarbons

Fractional distillation separates petroleum into more useful mixtures of hydrocarbons called fractions.

You need to know the different uses of each of the fractions.