By default, the iPad can’t make conventional phone calls – even if you opted for a model with cellular capabilities.
However, if you own an iPhone as well then you can make and receive calls on the iPad by routing through the phone.
On the iPhone, open the Settings app, select Phone and select Calls on Other Devices. Make sure Allow Calls on Other Devices is enabled. You can then toggle specific devices on or off – choose your iPad from this list to enable it. You can also use this setting to make calls from a Mac or another iOS device.
To enable the function on your iPad, open the Settings app, select FaceTime and flip the Calls from iPhone toggle on. As long as the devices are near each other and connected to the same Wi-Fi network, you’ll be able to start calls from the iPad as well as receive them.