This is a text for a one-quarter or one-semester course in probability, aimed at students who have done a year of calculus.
The book is organised so a student can learn the fundamental ideas of probability from the first three chapters without reliance on calculus.
Later chapters develop these ideas further using calculus tools.
The book contains more than the usual number of examples worked out in detail. The most valuable thing for students to learn from a course like this is how to pick up a probability problem in a new setting and relate it to the standard body of theory.
The more they see this happen in class, and the more they do it themselves in exercises, the better.
The style of the text is deliberately informal. My experience is that students learn more from intuitive explanations, diagrams, and examples than they do from theorems and proofs.
So the emphasis is on problem solving rather than theory.