A basic, working knowledge of Git - if you haven't used Git before, you should run through the Beginner and Getting Started tutorials at https://www.atlassian.com/git/tutorials. For a more comprehensive understanding of Git, check out the Git Essentials book from Packt Publishing.
Familiarity with the Linux/Unix command line - if you haven't used the Linux/Unix command line before, I recommend running through a basic tutorial such as https://maker.pro/linux/tutorial/basic-linux-commands-for-beginners, using the Linux Virtual Machine you created when you went through the Launch a Linux Virtual Machine tutorial.
Basic understanding of Python - the sample application for this book is written in Python, and some of the examples in later chapters include basic Python scripts. If you have not worked with Python before, you may want to read through the first few lessons at https://docs.python.org/3/tutorial/.