This is a LaTeX2e class. Begin your document with
\documentclass{cheatsheet}The document should be with quite small font and have 4 columns.
Then just write as normal.
The package mathtools is included, so amsmath is also included.
You need to have the cheatsheet.cls file in the directory where you use the class.
It is possible to install it permanently on your system, where you may use it from any directory, see LaTeX/Installing Extra Packages.
Summary; find/create a texmf or texmf/local directory, and place cheatsheet.cls under tex/latex/base.
Then you can use the class from wherever.
One option is included.
If defpkg is enabled, some more packages are included.
Enable it like this:
\documentclass[defpkg]{cheatsheet}There is also a math option for some math stuff.