Go to itead studio,
Select Download and download the eagle files
2Layer CAM for Eagle 5.x ITEADstudio_CAM for Eagle5.x.
2 Layer CAM for Eagle 6.x ITEADstudio_CAM for Eagle6.x.zip
2Layer DRC for Eagle ITEADstudio_DRC.zip2
Put the .drc file in the eagle DRC folder.
Put the .cam file in the eagle CAM folder.
With the schematic open, run the DRU check (tools:DRU I think, don't have it on this computer)
Address all the errors, make sure you understand the warning.
With the board open, run the DRC check - load the iteadstudio file and let it run, it will tell you about overlapping signals, signals too close, pins too close to the edge, pins not connected. Address all those. Some you may just approve, like unconnected pins if they are not actually used.
You will likely get a lot of warnings that are silkscreen related. If your component names are where you want them, those can be ignored.
To create the gerbers it's a 2-step process.
Select File:CAM processor, shoud bring up another screen.
On that screen, select File:Open Job, browse to the iteadstudio .cam file.
Then select Process Job. Close the CAM processor screen when done.
Now you will have all the files itead needs.
You can review them with a free viewer from www.viewplot.com
Zip all the files except .sch & .brd and send them to the address itead will send you after you make the board purchase.
I'm not looking at the eagle screens as I type this, so it may not be 100% correct, but close enough that you can find what's needed.