If you can follow the maths of things like Poisson distributions, the central-limit theorem, etc., then it's the modelling issues that are tricky.

Take a look at Dudley's Statistics for Applications from MIT's Open Courseware - http://ocw.mit.edu/courses/mathematics/18-443-statistics-for... - is supposed to be very thorough and easy to follow, but warning, it's based on an expensive textbook.