Buff is a machine that is relatively beginner friendly. This write-up is similarly geared towards beginners to Hack the Box(HTB) and Pen-testing/Ethical Hacking in general. Things like hacking phases and what a shell is will be explained more in-depth than the average HTB write-up.
This machine is also great for beginners because it employs techniques that are common in Hack the Box and other vulnerable machine platforms. Things like starting a netcat shell and a python web server is done several times, which is great practice.