Well first, you have to have a decent broadband ISP connection with a static IP address. Most household cable / DSL accounts are dynamic IP address, so it will change your IP number on you from time to time. Also some accounts specifically forbid you from running a public server. Check your particular situation.
You can get around the dynamic DNS thing by signing up with a Dynamic-DNS Routing service, where you have a domain name, and the service "chases" your account and updates the IP in their routing to whatever your current IP is.
OS X comes with web-server and FTP server software, you will need to learn to configure it: Google for many resources.
BUT: You put .5 terabyte of goodies online, you're going to get swamped by friends downloading whatever, hacked by robots, idiots and scoundrels, then booted offline by your ISP for exceeding account limits -- or charged $$$ for bandwidth overages.
Why bother, when you probably get some web space for free with your ISP's account, or you can buy space for $5 to $15 per month from someone who will maintain the software, the hardware and the connection?