Not able to send messages to all contacts

my new iPad will not send instant messages to non-Apple contacts. How do I fix this?

You will need an iPhone. Then use iOS continuity to pair the iPad with the iPhone to use the iPhone‘s sMS/MMS texting capabilities. See https://support.apple.com/en-us/HT204681

SMS and MMS messaging requires a cellular telephone voice connection. No iPad is capable of connecting to a carriers voice network so cannot natively send or receive SMS/MMS texts