If you download the forge tools (though the reference data is out of date) in the downloads section, it comes with some basic tutorials (though these are in nice pdf files). This site might help as well. However, a lot of the specific information tends be on the forum posts here. If you're new to modding I highly recommend you start editting the files of the existing factions first, as you need a decent idea to how the files work for making new factions.
