that is not so smart of a question to ask here.
Check out
http://www.irchelp.org/ and you might be able to find answers. As for here, you question is too broad.....an its jjust not the place to ask it. mIRC is designed for chat, and its "file sharing" features.....are just....features
If you want to learn how to download, go to the source, an just for hints...this isnt the source.....for that