Hitman Beta FAQ on the official Hitman website has details on beta testing of the upcoming assassination game, which launches this week for PlayStation 4 and next week for PC. They include a beta launch trailer to show this off, and they offer the following explanation of what's included and how to participate:

WHAT’S INCLUDED IN THE BETA?
The HITMAN Prologue. That’s the very beginning of the game, set at a top secret recruitment and training facility. The Prologue revolves around how Agent 47 joined the ICA and shows the first time that 47 meets his long-time handler, Diana Burnwood.

The Prologue contains an introduction to the gameplay features and mechanics in HITMAN, and two free-form training hits. You’ll be able to replay each hit as many times as you wish throughout the beta period to complete the challenges and the multiple ways to take down your target – as you would expect.

HOW DO I GET ACCESS?
The only way to guarantee your access to the HITMAN Beta is to pre-order the game digitally on PlayStation 4 via PSN or PC via Steam. Alternatively, you can pre-order the Collector’s Edition.
Access to the HITMAN Beta is available for the pre-orders of the Full Experience, Intro Pack and Collector’s Edition.

PlayStation 4: Full Experience / Intro Pack
PC: Steam Store Page
Collector’s Edition: SE NA Store / SE EU Store / Full details