I don't know your major, but let me recommend this book:

Hamilton. 1994. Time Series Analysis. Princeton Univ Press.

This book seems old, but still all you need to know about time series is covered in one place. At a first glance, this book seems too technical to follow, but actually it is not so.

Another possibility is not the book, but the book-length treatment of time series:

John Cochrane's lecture notes (see the attached).

You don't need much math, but if you are familiar with math, you can get more out of these.

Thank you very much. My major is Petroleum Exploration.