If Find My iPad is ON, (It should be on by default) then go to www.icloud.com/find then log in. It should show you it's location.
If your iPad is nearby you can play a sound on it. If it's not nearby and you think someone else can find it you can put it in lost mode. Lost mode will add a passcode to the phone if you don't have one already and it will display a message and a number to call on screen.
You can also erase the device on find my iPad . If you erase the device, it will keep your Apple ID information stored on it so you will have to reactivate it with your Apple ID and password so no one else can use it even after you erase it. You will not be able to use the Find My iPad features after you erase it. If you find your device after you erase it and you have an iCloud backup available you can use that backup to restore your data
If Find My iPad is OFF, there will be nothing to help you find it so you will have to look for it manually. Try retracing your steps and if you went into any stores, ask the employees at the stores. You can also talk to a friend and see if they found it and if not they can help you look for it.
You can learn more here: If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support
