Using the Search option
The easiest way to find features and principles which interest you is by using the Search option (on the Browse Mode menu). For instance, if you are looking for features that illustrate the Rock Cycle system, Just type "Rock cycle" in the search window and click "go".

Using filters
If you want to be less specific than in the previous example, you might want to use the "Subject" filter to find all features in earth science. If that's too general you can continue and filter the results by using the "Audience" filter to find those features that are earth science middle school, and continue with the "Category" filter to reduce the list to features that are visualization tools for middle school earth science.

Browsing through connections between features and principles
After finding a feature you are interested in, and viewing its details, you can click on one of the Pragmatic Principles connected to it, and learn more about the general rationale which guided the design of this feature. For instance, if you click Manipulative animated 3D illustrations in Geo3D, you'll see that it is connected to a few Pragmatic Principles. One of them is Reduce visual complexity to help learners recognize salient information. Clicking on this link would show the details of this design principle, and would also show other features connected with this pragmatic principle. Many times viewing other features related to a principle helps understand the scope and meaning of the principle.