Its an old school chat protocol. You can try it for yourself kiwiirc is a website that lets you chat with IRC. You need to pick a network, Rizon is a good network to start with. There are a bunch of different commands you can use but the only ones i found useful are /msg to send a message and /join to join a channel.

For the downloading part you need a client that supports XDCC, and then you can use these commands with your bot of choice