I'm trying to understand the Homotopy Type Theory book. I find myself completely lost in Chapter 2, especially when it starts using higher groupoids.
What is the recommended background for this book? I once studied abstract algebra (and even remember a bit) same with topology, but not category theory. I skimmed a topology book recently to refresh my memory, but I'm realizing that the topology in the HoTT book is algebraic topology and I haven't studied that before.
My general question how can I fill the gaps in my background knowledge so that I can make sense of this book?
More specifically for Chapter 2, what is a good introduction to higher groupoids? Should I expect to learn about those by studying algebraic topology or category theory?