Get your IP Address, go to www.my-ip.com or some website that will tell you what your IPAddress is (unless you know where you can find it on your computer). That's the IP you will have others connect to.

1) Send them your Open Source Files and Levels now.
2) Open the Main level up
3) Hit Run
4) Server enter "-sv -cl" and hit RUN
5) Client enter "-cl -ip 000.00.00.000" and hit RUN
6) Ta da...should be running together.

This is all assuming your code is prepared for Multiplayer gaming, otherwise the story could end up differently.