The next post linked in this series is "Focus your Uncertainty". It seems to be a sort of warm up for Bayes' Theorem. I think its about time we did a whole lesson on Bayesian Reasoning.
Instead of reading the next post in the series, I'd recommend you read "An Intuitive Explanation of Bayes' Theorem" OR "Bayes' Theorem Illustrated" which both do a good job explaining Bayes' Theorem in different ways. Different people learn in different ways, so if one explanation isn't working for you, try the other post and see if that makes more sense. In any case, we'll cover it at the meetup and why its important to know.