The community forum has great real world information, with many helpful super-users contributing lessons learned, best practices, and solution recommendations.
Cambium College is helpful for basics on the underlying technology and principles used across the industry.
The webinar archive and YouTube channel are a good ways to stay updated on new products and best practices.
The technical training site provides a deeper dive into specific Cambium products, new firmware release features, and access to live, classroom certification courses.
The support site (specifically LINKPlanner) hosts useful information within user guides, installation videos, and design/management tools. The LINKPlanner User Guide has a wealth of information on wireless and products.