Buy the main book: The main book, with rules on how to play, 3 starting missions, as well as a large adventure - This book is what you need to get the full Rangers Experience
https://www.drivethrurpg.com/product/257695/Rangers-of-Shadow-Deep-A-Tabletop-Adventure-Game
Modiphius has produced a deluxe, hardcover edition https://www.modiphius.net/products/rangers-of-shadow-deep The pdf version of the Modiphius layout: https://www.drivethrurpg.com/product/298580/Rangers-of-Shadow-Deep-Deluxe-Edition
1 scenario A on-shot scenario involving a werewolf mystery https://www.drivethrurpg.com/product/261465/Rangers-of-Shadow-Deep-Blood-Moon?src=also_purchased
4 scenarios A larger 4 mission story where you steal into a temple to defeat a dark wizard
https://www.drivethrurpg.com/product/270195/Rangers-of-Shadow-Deep-Temple-of-Madness
4 scenarios A larger 4 mission story where you play both a beginner ranger and your veteran https://www.drivethrurpg.com/product/284650/Rangers-of-Shadow-Deep-Ghost-Stone
2 Scenarios A 2 scenario story where you escape jail
https://www.drivethrurpg.com/product/294882/Rangers-of-Shadow-Deep-Incinerator
2 Scenarios A 2 scenario story including new animal campion rules https://www.drivethrurpg.com/product/323235/Rangers-of-Shadow-Deep-Menagerie
4 Scenarios The first 4 Scenarios of a larger Mission for high level (10+) Rangers.