Ranger Handbook

• Ranger Guide Contains Information On A Variety Of Topics, Including Insights From The Basics Of Army Operations, To Learning What It Takes To Be A Solider With Great Leadership Qualities And Character
• U.S. Army Ranger Handbook Includes Chapters On Leadership, Missions, Movement, Patrolling, Battle Drills And Mountaineering
• United States Ranger Handbook Is Full Of 444 Pages Illustrated
• Army Handbook Is The Perfect Gift For Those Who Love The Rich History Of The U.S. Army
• Ranger Book Sized At 5 1/2"X8", Made To Fit Into Your Gear Pack

This will be your bible while you're at Ranger School. They give you one, but it is smart to have a solid understanding of the books contents before you arrive. You can also get a free PDF from Army Pubs or use the Living Doctrine Supplement. Link below. The most updated versions are always there. 

Army Publishing Directorate

Ranger Handbook, April 2017, TC 3-21.76

Ranger Handbook, February 2011, SH 21-76

Living Doctrine Supplement

Also, there is an audio book version on YouTube.