Cycloalkanes are made up of only Carbon and Hydrogen atoms all singled bonded, just like straightchained alkanes. But since cycloalkanes are in a ring they have a slightly different formula (essentially two less H atoms in the molecule).

The general formula for Cycloalkanes is:
CnH2n
The lowercase n represents the number of Carbon atoms in the cycloalkane. So for example, if you has a cycloalkane with 7 Carbon atoms the formula would be C7H(2*7) or C7H14.

In this video we look at cyclopropane, cyclobutane, and cyclopentane. But the general formula applies to other cycloalkanes.