Using Hack requires installing HHVM. Once HHVM is installed, your project needs to be configured to run the Hack typechecker.
Follow along the HHVM installation “getting started” guide, which will guide you through getting HHVM and a webserver set up to run plain PHP. Pre-built packages are available for most Ubuntu and Debian systems — it’s not hard to get working! The guide will walk you through it.
Run Hack on HHVM
Now that you have PHP running on HHVM, get Hack running on HHVM. The Hack installation docs describe how to get the typechecker running on your Hack code. Make sure not to skip this step, or you’ll miss a bunch of type errors!