The base FHIR Specification is a platform specification - a specification on which all sorts of different solutions are built. The specification focuses on defining capabilities, and creating an ecosystem. National standards, vendor consortiums, clinical societies, etc publish "implementation guides" that define how the capabilities defined by the FHIR specification are used in particular data exchanges, or to solve particular problems. Here is a list of some of the implementation guides defined by the FHIR community:
In addition to this list of Implementation Guides, the full FHIR registry is at http://registry.fhir.org.