In the specification, you have to read it carefully to understand the purpose. In the Getting Started guide, there's a diagram that lifts the confusion a little better.

The Model Context Protocol helps you build a translation layer between an LLM system, and some other system or data resource, such that the LLM may operate that system on your behalf or scan that resource for additional context in generation. You wrap a resource or some system local or external with an "MCP Server." The LLM can operate that MCP Server, which in turn operates the system or reads the resource.

The text kind of says that... but the diagram in the guide drives it home. The diagram or some form of it should probably be added into the top page of the spec.