How Do I Text To an Android Phone From My iPad?

I found that SMS was turned off on my iPhone. After I turned it on I was able to send Messages to an Android phone. When I tried to send a message from my iPad it didn’t work and I could find NO setting to turn SMS ON. How can I send a message to my son who uses a Samsung phone? Apple notes tell me:
1) in messages—not registered with iMessage
2) in FaceTime—phone calls not available.
Apple gives no instruction on how to do this.
Why must Apple make it so difficult to communicate with non-Apple devices? Some time ago Apple learned that they must live alongside Microsoft. And they did it. Now Android is the foe and they won’t accept that. I just want to be able to text my son’s Samsung from my iPad, and know how to set it up if this is required.
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Diana