Let's say, you just finished making a model and you want to use it in other applications.

First thing you want to do is, is make a new folder in a directory of your choosing. Now we have a place to export to. Name it anything you like. I'm making mine in the home directory, and named it, of all things, new folder.
Navigate to File/Export/Wavefront (.obj)

A dialog box will open. Navigate to the folder you just created, and name the file. Then click on export.

Hint, when you click on export, the first time. Under, (look in). You will see your folder. Click it again to export,
and your dialog box will disappear.
In the status bar, you will see the status of the export. (If that makes sense.)
Navigate to your new folder and look inside.

Note, the material file with it.
One thing to remember. Keep the material file, and the object file, in the same directory. Otherwise, no worky.
Now, open Blender, and delete the cube.

Navigate to File/Import/Wavefront (.obj)

Navigate to your new folder.

Inside new folder, select the .obj, and click on: Import Wavefront OBJ.

The material file will import with it. As long as they are both in the same directory.
A dialog box will appear. Except the defaults and click OK.

As you can see, it imported, with all its materials.

Now, you can use those model in othere applications.

Cheers!
You can start building that prop library.
