how do I send text messages to people without an iphone

SMS/MMS messages are a Cellular Carrier feature - and for you to send them from your iPad you will need an iPhone with Cellular Service plan that includes SMS messaging. Anyone with a phone that can receive text messages can then send or receive messages to/from you - on either your iPhone or iPad.

If you don’t have an iPhone associated with your AppleID, you are limited to sending and receiving messages via Apple’s own iMessage service - and are therefore limited to sending and receiving messages to/from Apple devices.

If you have an iPhone - and that both your iPhone and iPad are logged-in to iCloud with the same AppleID, on your iPhone:

Settings > Messages > Text Message Forwarding - enable for your iPad.

If you don’t have an iPhone and the receiptent doesn’t, then you both could use Skype, Google Hangouts, WeChat, Viber or another internet messaging service that offers cross platform apps.