OK, so the course packet of notes that you've installed is enough to get you started—you can click on e.g. 01_introduction.Rmd or 02_get_started.Rmd and begin taking notes there if you wish. (The file names are keyed to the chapters of the book.)
However, you should also be able to access the template. I fixed this problem just yesterday, so I'd ask that you try one more time to install the socviz library and go through the File > New File ... > R Markdown steps you do in the video. So, from the console,
install_github("kjhealy/socviz")
Then quit R Studio, relaunch, and
library(socviz)
(That step isn't required, but I'm trying to be thorough.)
And then File > New File ... > R Markdown