That looks interesting, although it is 3 hrs. I like this ~45 minute intro to the concept, which seems a little more Turing-accesible:, in that it shows how you can implement addition and multiplication in the system, which is a lot:

https://youtu.be/OLH3L285EiY

successor function: given a number, get the next number

try this in Python:

zero = lambda f: lambda x: x

one = lambda f: lambda x: f(x)

two = lambda f: lambda x: f(f(x))

to_int = lambda n: n(lambda i: i+1)(0)

succ = lambda n: lambda f: lambda x: f(n(f)(x))

three = succ(two)

four = succ(three)

to_int(four)

So that's just counting, the Church Numerals, where it begins.