I've been reading Lectures on dynamical systems by E. Zehnder. This book is undergraduate text and its intoductory chapter is about ergodic systems (with Birkhoff's theorem proved), which I found interesting.
I would like to know what is the good reference for further reading on ergodic theory (not necessarily an undergraduate text), based on topics that are covered in this book.
(Similar questions were posted, but the most of the proposed books seemed difficult for reading.)
Also, I would like to know more about applications of ergodic theory and does there exist any textbook in ergodic theory?
Any help is welcome. Thanks in advance.