In eagle, when you define the pads for the component footprints, the solder mask is defined as a stepback from the pad. This is shown for the top of the PCB in the tStop layer.
When sending your board to a fab house, you will need to supply a gerber for the solder mask. I believe the standard CAM processor for eagle outputs this layer as an .stc file.
Your board producer will also probablly prefer an excellon drill file, rather than a gerber for the hole locations. Eagle produces this as a .drd file.
Look in the eagle documentation under "CAM Processor" and you will find descriptions of the various layers, and how they are used. The best thing to do, is to ask your board manufacturer what files they need. Some who are use to dealing with Eagle, will acually prefer if you just send them your board file, and they will produce the gerbers and other info they need.