Most users will prefer to use Proton provided by the Steam client itself. The source code is provided to enable advanced users the ability to alter Proton. For example, some users may wish to use a different version of Wine with a particular title.
Getting Started with Proton from Steam Play
Make sure you are opted into the Steam Client Beta!
Proton requires graphics drivers that are more recent than what is typically packaged in most distributions; please read the list of requirements and quickstart for Ubuntu 18.04 users: https://github.com/ValveSoftware/Proton/blob/proton_3.7/PREREQS.md
Install and play games! Please refer to this post for more information: https://steamcommunity.com/games/221410/announcements/detail/1696055855739350561