This site, by Oscar Bonilla, gives an intuitive introduction to Bayes’ theorem:

http://oscarbonilla.com/2009/05/visualizing-bayes-theorem/

Here is a simple one-page tutorial packed with examples and visual aids to help clarify Bayes’ theorem and how it works:

https://www.bayestheorem.net/

This super site provided a Bayes’ theorem calculator.

http://statpages.org/bayes.html