This is an extreme condensation of the Servant tutorial. If you've read that tutorial before and don't want to read it again, you might find this useful.
To try running a server, run main, or main2, or main3, etc. from Server.hs. Some of those commands have comments describing ways to query the server.
To try running a client, run Client.run. See comments attached to it for how to run a server the client can query.