Although everything you need to know about songwriting and learning how to write songs is contained within the pages of this site a great song writing book will also help you understand the craft a bit better.
You may have heard people say you can't teach someone how to write a song. This is complete rubbish. Songwriting is a skill you CAN learn and with enough hard work even excel at. Like any craft it will take time and practice but you will get there.
So let's take a look at some songwriting books that will help you on your songwriting journey: