There is no Google Play Store app for iPad, but you can still download Android apps on your iPad. There are two ways to do this:
Use an Android app emulator like Bluestacks. This will allow you to run Android apps on your iPad, but they won't be as well optimized for the device's larger screen.
Use a service like AppRadio that will let you stream Android apps from your computer to your iPad. This option will give you the best performance, but you'll need a computer with a good internet connection to use it.