I don't think you are supposed to use these patterns directly, but they describe common solutions to problems that let us use a shared language when discussing code. If I say that 'we can replace this with something like a flyweight', I expect you to know what I'm talking about. I'm not expecting you to implement it "by the book" but we can discuss it without me having to explain wtf a flyweight is, how it works, and how it applies to this situation.

That being said, these days there are much better resources out there for this stuff.