Oke, I give you a step by step guide:
lets say, your mod file has the name "girl.swf"
1. create a new folder inside the mods folder
2. give it a name, for example "myNewMod"
3. Open CharacterFolders.txt
4. Add the line: myNewMod:MyNewMod
5.go to your new folder (myNewMod)
6. insert girl.swf into the folder.
7. create a new file called "mods.txt"
8. add this line to mods.txt: girl.swf
Thats about it.
If you want to load multiple files at once, just put them all into the same Folder and add all filenames to mods.txt
If you want to load a png hair import, you can also put it into a folder and rename it to "hair".png.
In this case you don't need to add the file name to mods.txt