Ipad with Cellular Data Capabilities

One that has cellular can use a SIM from a cellular carrier and have a data plan (you would have to pay for) and allows you to use data when away from a source of wi-fi data. That is the easy explanation. Do you need any additional information?

Note: A cellular iPad has GPS hardware whereas iPad Wi-Fi only do not.

You can use iPad to text any other Apple devices.

Using iPad to text Android devices, you also need to have an iPhone using the same Apple ID.

Yes, that's correct.

More info here => How to forward SMS/MMS text messages from your iPhone to your iPad, iPod touch or Mac - Apple Support

Assuming your iPhone has a valid SMS/MMS plans from your carrier.

You're welcome, enjoy.