You can access the Agile Manager Help directly from the product.
In the upper right corner, click the Help menu icon, and select Help Center or Help on This Page. Both menu items will take you to the same Help Center, but Help on This Page opens a description of the Agile Manager page you're currently looking at.
You can also access the Help outside of Agile Manager using this link.
If you're just getting started, you might want to take a look at some of the movies in topics linked from the Home Page or read through the topics on project and backlog item lifecycles.