I dunno, this book bothers me. Tells me to get the parts, make he circuit but doesn't explain why these parts work why I need this particular version of the component.
Because of that remark, i downloaded the book and had a look at it.
As these books go, this one isn't bad at all.
The transistor is discussed a few pages further (page 101), but within this project.
No doubt not everything that can be told about transistors is discussed here, you can fill entire libraries and still not cover everything.
Read the entire section before you start building or experimenting with your project.
And start reading from page 1, don't start at the first project that interests you (i'm not saying you didn't or blaming you for anything here).
The further you progress in the book, the more is assumed you read the previous content and learned from that.
Maybe tedious, but that's how the book (any book) was written.