In principle, FREDURES is organized as a hierarchy. In practice, though, if you cannot find what you are looking for at one level of the hierarchy it is always worth checking at another level.
The red search box searches the major sites offering free educational resources on the internet.
The yellow search boxes search sites listing free educational resources in the four basic categories (arts & humanities, social sciences, pure sciences and applied sciences).
The blue search boxes search subject-specific resources, e.g., "history" on the arts & humanities tab.
The green search boxes are still under development. They will search for specific topics inside each subject, e.g., "American history" on the history tab.