Here are instructions for getting Hail set up as a user:
https://hail.is/docs/devel/getting_started.html
Here are instructions for building Hail, docs and running tests as a developer:
https://hail.is/docs/devel/getting_started_developing.html
Most of us use IntelliJ Community Edition for Scala development. After cloning the Hail repository, in IntelliJ you can “Import Project”, select the build.gradle file in the hail repo, and check “Use auto-import”.