Marco Codes' YouTube video explains the Model Context Protocol (MCP), an initiative by Anthropic (creators of Claude) that allows language models to access external data. The video demonstrates how MCP enables Claude to summarize GitHub commits, a task it couldn't perform without this protocol. MCP involves a client (like Claude Desktop), the Claude language model, and an MCP server that acts as an intermediary to access data sources like GitHub. The server exposes its capabilities as "tools," which the client can request Claude to use. This process involves multiple steps where the client first asks the server for available tools, then sends the user's query to Claude, which in turn requests the client to use a specific tool from the server to retrieve necessary data. Finally, the client sends the retrieved data back to Claude to fulfill the original request. The video also shows how to configure Claude Desktop to use an MCP server and highlights the existence of pre-built reference servers for various data sources.