5. Get the device ID's of all your devices

To test your app on your iPad, you must specify its device ID (that is, its UDID).To get your iPad's UDID:

Plug your iPad into your computer.
Launch iTunes
Select the iPad in iTunes.
Click the Serial Number label. The label changes to Identifier (UDID).
Press Command+C to copy the device ID to the clipboard.
Paste the device ID into a text file. It should be a very long code with both numbers and lower-case letters, but no hyphens or other characters

When you build your app with App Studio, you will have an opportunity to preview the actual app on one or more iPads before submitting the app to the App store. This preview will include your app icon, app name, and the fully functional app. To preview the app, you will need to provide Apple with a list of udids (like serial numbers) of each iPad on which you will want to preview your app. here is one way to discover the udid of your iPad:

Attach your iPad or iPhone to your Mac with a USB cable.
Launch iTunes.
Select your device in the upper right area of iTunes.
In the summary section, locate the serial number of your iPad.
Click the serial number, and it will change to the udid.
Press command+c to copy the udid, and then paste the udid into a text file for safekeeping. (you don’t select the udid before copying---just press command+c and the idid will be copied to the clipboard).
Repeat for each iPad, iPhone, or iPod that you will use to preview your app.
Go to the Apple iOS developer site, you will need to sign in with your Apple id.
Click Certificates, Identifiers & Profiles
Click iPad or iPhone under Devices on the left side options
Click the Plus icon in the upper right corner of the window to add a device.
Enter a name and a udid for one of the devices on which you will want to test your app. This is the information you gathered in step 6, above. To enter the information for another device, click the plus icon. When you have entered a udid for each device that you need, click the continue button.

You should now have a list of each device on which you will want to test your app displayed in the devices section of the Provisioning Portal.

Click Certificates, Identifiers & Profiles