A regular expression is useful to match strings of text, when you write programs or find particular character, word or pattern. That's simple you are supposed to know about regular expression.
However, There is a book about regular expression, that tittle is Regular Expressions Cookbook by Jan Goyvaerts, Steven Levithan. It has 612 pages over 9 chapters. In this book, you will learn a lot of regular expression practicals, but readers ought to have programming skill. This book uses "Cookbook" on book title, but material in book is not easy to understand, if reader is newbie developer.
If you read this book, You will know it easy to find each topic and idea. You can read topic which you are interested. You don't need to read all.