The essential concepts of git are treated in the first four chapters, they should be read thoroughly and carefully, in order. Chapter 2, Chapter 3, and Chapter 4, treat the cases, respectively, of one, several, and many collaborators, with very different organizational models, but the concepts are universal to all three models.
Eventually you will find more intricate topics in Chapter 5 and Chapter 6 necessary or useful, and maybe both. Chapter 7 explains ways to backup and correct mistakes. Chapter 8 is a grabbag of short topics that do not fit naturally in the early material and would have just been a distraction. At some point familiarize yourself with what is on-offer there. The appendices contain technical information that might change over time, in addition to reference material.