How do I text from ipad to non iphone user?

If you have an iPhone, set up text message forwarding. Settings > Messages. You can then send messages from your iPad using your iPhone as a relay.

you could also use your carriers email to text gateway. Ask them for details of the email address.

The simple answer is, you can’t. That is, for non-cellular models. Meaning you can only iMessage if you have an iPad with just Wi-Fi. If you want to text people, you would need an iPad with Wi-Fi + Cellular.