To become a playtester, enter your name, email address, and how many keys you need for your group on the Dev Blog page of this site. I will add you to the mailing list and then send your Steam access keys via the submitted email.
These keys will give you access to the beta branch build in Steam (in your library: Adventure Portal -> Properties -> betas -> select testing). This will also give you the full game when it comes out -- my thanks for testing :)
Test away! I hope it works well for you. I ask that players take notes for feedback and then visit these forums to report their thoughts. I will have another thread for posting the feedback. You can also drop into Discord to report what you think.
So that's it, thanks so much for checking out my program!