Before you begin, you need to have some basic knowledge of how Linux works. That is to say, you need to know what a desktop environment is, or how to work with a package manager. You also need to know how to troubleshoot basic errors. Knowing the very basics of what a for loop is, or what Switch–Case is, would help you learn faster.
Also, if you are new to PowerShell, reading the first chapter is recommended. This chapter contains a couple of important guidelines for working efficiently with PowerShell.
The book also assumes that you are working on either Ubuntu or CentOS. While PowerShell constructs themselves do not behave differently with different Linux flavors (or even different platforms), the installation—and sometimes the configuration—may be different on different flavors of Linux.