Ask HN: How does MCP tool calling work?

I found it's a bit confusing on how exactly the tool calling work, where does it work ?

Let's say we have a server, with an ai agent configured with tools.

We also have client, which call openai api , and it's also provided with mcp servers.

So when we prompt, how does the whole mcp servers, tool calling resolution and tool execution actually work ? Where does it execute ?