Forgot:

What too creates mods?

To make a mod for a server is as easy as making a mod - just make sure the servers using files that are modified with the mod. Its that simple!!

How to build one is not however. There are lots of tutorials in the tutorials forum, help in the general editing forum and so on. A good place to start is the thread that says its got it all in general editing - its stickied at the top. It tells you lots of info whilst also providing links to topics of interest.
We cannot really and logistically teach you hand held how to do it - cause imagine the thousands who come to mod here - if each one wanted a walk through - then it would be a full time job. Also - you need some sembalence of capability to mod too. If you aren't willing to spend several weeks, using many hours a day in learning HOW to do things without much to show for it - then modding is not for you!! It will take a LOT of time to make anything of reasonable size - and it may not even work - as lots of crashes are about.

Freelancer explorer is a tool for building systems that removes any difficulty on the creation part of it - its available ain the downloads section - as is the detailed tutorial that goes with how to use it (search downloads again!).

You are best off with the SDK first - cause the files in freelancer are compressed and encrpyted. The SDK is basically all those files decrypted and decompresssed - which makes it all alot easier. Once that is done they can be opened and edited with a simple text editor! From then on its a combination of reading tutorials, playing around with things, and testing.