Generally speaking (I'm not an expert for all those things):
You need a 3D modeling program, for example 3DstudioMax. Try some tutorials in the internet, start with easy things as simple geometric forms. Then try to build some houses and furniture. (I'm not kidding, try to build a sofa, and if you can do that, you can try a simple spaceship!)
Then you need textures. Textures are pictures, you can use png or DDS formats IIRC, you have to use a certain resolution (depends on the details you want). Parts of the picture are used for parts of the ship.
Then there are glow maps, shine maps, normal maps and... I think I forgot one.... Whatever. Those are additional files for effects. They basically work like the textures.
All things you need to know about nav points, mission desogn and stuff you can learn here in the forums. There are a lot of FRED tutorials (the mission editor for FS2).
I REALLY suggest you start with making missions (with existing ships and without complex scripting) just to learn to use FRED.
If you manage to do that you can try to learn 3DsMax and do some ships and stuff.
But it is a lot of hard work, FREDding is the easiest part, but you know: There is a reason why our team consists not onnly of one or two people but of... yeah... ahemm.... I don't know exactly.... maybe a dozen people?
EDIT: You will need to learn something about FS2. Karajorma made an excellent FAQ. Here's the link:
http://homepage.ntlworld.com/karajorma/FAQ/intro.htmlThere is also a big part of these forums for FRED:
http://www.hard-light.net/forums/index.php/board,89.0.html