These are cool examples, but they're probably not the best examples to study if you're new to Mathematica. A lot of these examples are really meant to show off and be fancy. I recommend looking at the examples in the documentation:
The documentation is also great because it's available in Mathematica itself. You don't need to copy and paste code. The documentation is a live document that you can play with and make changes to.
The code looks like it written fairly early and didn't reflect some changes. For example, "Library" isn't really a kind of Entity anymore. It's been broken up into "LibraryBranch" and "LibrarySystem". So the first piece of code for the Library example probably should be
allLibraries = EntityValue["LibraryBranch", "Entities"]
Thank you for letting us know about this issue. I will contact the relevant people so that these examples get updated.