Calculus Based Probability.
To learn this section you need to know about Integral calculus (and Differential calculus of course) and/or finding the area under a curve and some integration techniques. like U-substitution, Integration by parts. You an learn these things from the relevant pages of this book.
Calculus plays an very important role when it comes to probability as well. When you learn discrete probability distributions like binomial distribution you don't have to deal with continuous data because all the data are discrete. Let's imagine situations when you need to calculate continuous data, like the height or weight of a person. You cannot practically measure it 100% correctly. Meaning there is no probability of living a creature whose height or weight is exactly 2.000... meters or a exact value like that. Think about it a little bit.
When calculating things like that, you need to make an interval so you can check whether the person you measuring is around 2. like 1.95 - 2.05. So when you calculate the probability of this kind of situation. You need something other than discrete calculations.
This is where calculus comes in.