If you are playing with 2 or more people, private hosting generally doesn't work. With just a single remote player, you should be able to share a game hosted on your local server. *
To host a game from your own LAN, you need to log into your router and set it up to forward traffic on port 25565 to your PC.
You can try just share a SSP game with the "Open to LAN" option, but I don't know if that uses a consistent port, otherwise use the FTB launcher to download the server for your pack and run that.
use a site like "MyIP.com" to find out what your IP address is and share that with your friend to connect to.
* Locally, we get our internet via ADSL, and the bottom end package is a 2Mb package. which is pathetic, but does actually support several outgoing players with no issue. The problem comes about because the "A" in adsl is asymmetric, and the upload speed - which handles the bulk of the traffic when running a server, is only 512Kb. A 512Kb uplink is fine with a single player connected, but becomes noticably laggy with even 2 remote players. If your uplink is 1Mb or higher you might be able to handle more players.
