Hamachi connects people to a LAN (Local Area Network), but what you really want is for people to connect through WAN (Wide Area Network, ie the Internet), unless you don't want random people signing up to play.
If you don't want random people and just your friends, then just use Hamachi.
The IP you'd use is the one that Hamachi gives you.
If you want the WAN, you'd need to get a STATIC IP address and must have a router to open your ports.
And it'd depend on what router you have, but
portforward.com has lots of tutorials of (all?) routers.
Regardless of what you do...
You /might/ need to have you and your friends edit their hosts files in order to connect to your server.
Edit:
Also... if you don't have a router... USE HAMACHI