If let's say that the real VPIP of someone is 50% and we have just 20 hands on him, how to know on a confidence interval of 68% or 95% or whatever, what the differences are going to be from his real VPIP? I want to understand what a good sample size is for using to make educated guesses on our opponents.

I was watching this very interesting video which talks about this stuff, but doesn't talk on how to calculate this yourself for any sample size or other VPIP percentages. Video: https://www.youtube.com/watch?v=hbQ9Jlj9bOE

I want to be able to calculate this stuff in any confidence interval I want with any sample size or VPIP. Could you tell me any videos or articles which I can use to learn this stuff? I searched but everything seems very confusing...