After starting the program, you need to import a obj file first by clicking on "Load .obj".
The program will output now something like this in the textfield:
objload "sack.obj"
objskin pSphere1 "texture.jpg"
objskin pCylinder1 "texture.jpg"
objskin pTorus1 "texture.jpg"mdlscale 100
"Objload" loads the obj the textures should be assigned to.
"Objskin" assigns to a model group a texture.
"Mdlscale" sets the scale of the model in %.
Make the changes you want and press on "Save .cfg". A file named "obj.cfg" is saved to the location of the loaded model.
Create a folder (the folder name should relate on the model) in "/packages/models/" and copy&paste the model, obj.cfg and the texture.
For the example the folder structure would be like this:
/packages/models/sack/sack.obj
/packages/models/sack/texture.jpg
/packages/models/sack/obj.cfg
Finally you either need to add to the cfg of your map or to "data/default_map_models" a similar line:
mmodel "sack"
This tells PAS which subfolder in "packages/models" to look for the model.
You can insert "../" for the model or texture name to tell PAS the texture is located in a folder above.
You can find more model commands here: http://sauerbraten.org/docs/models.html