Our thinking is that prompts will generally be a user initiated feature of some kind. These docs go into a bit more detail:

https://modelcontextprotocol.io/docs/concepts/prompts

https://spec.modelcontextprotocol.io/specification/server/pr...

… but TLDR, if you think of them a bit like slash commands, I think that's a pretty good intuition for what they are and how you might use them.