Hi jcm53byu,
You started from a great resource: What is the difference between iMessage and SMS/MMS?
Regarding sending media content to non-iPhone users be sure the SMS/MMS option are turned on. Navigate to Settings > Messages and under the SMS/MMS section toggle on MMS Messaging.
If needed, the article here can assist as well: Send and receive messages on iPhone
Should you continue to have an issue, reach out to your cellular provider to ensure the feature and your account are provisioned to send SMS/MMS messages.
If your carrier states all is well, follow the steps here: If you can't send or receive messages on your iPhone or iPad
Cheers.