How to Teach Functional Programming to New Developers

When you're bringing on say new developers to the team or even to the project, how do you kind of teach them this pattern? I think first of all, we start to reference to some book with some principle. So they get really bothered and also when you work with a small team that use the same part in the same principle - it looks like only one programmer write all this code. And yes, I think we also have some channel inside our discourse message where we can communicate with each other the name of this channel helping Hands.