The document provides guidance on how to combat the first 90 days as a new product manager. It outlines the 3 P's of onboarding to focus on - Product, People, and Processes. It recommends spending the first 30 days observing and learning about the product and users, the first 60 days evaluating the product and building collaboration, and the last 30 days starting to drive your own strategy and deliver value. Key tasks outlined for each phase include deep diving into product data and customer needs, building relationships, owning small features, and aligning roadmaps. The document also provides tips for dos and don'ts of onboarding like focusing on the big picture, asking questions, avoiding comparisons, and being willing to fail fast.