how do i set my ipad to receive same messages as my iphone?

If you have an iPhone - and both iPad and iPhone are signed-in to iCloud with the same AppleID - to send SMS/MMS messages (green bubbles) from your iPad you must explicitly enable Text Message Forwarding for your iPad on your iPhone...

On your iPhone:

Settings > Messages > Text Message Forwarding - set to ON - and explicitly enable your iPad from the list of devices.

Also ensure that Messages in iCloud is enabled on both your iPhone and iPad:

Settings > [Your Name / AppleID] > Messages - set to ON

Well to add a number, go on your iPad, into settings, then click on your account with your logo and name, then go to numbers, phone numbers, emails, and there should be options to add a number or an email

Then when you get there, there should be a option that shows your Apple ID, and below it, it says rechargeable at: and your email. Just click your email that’s showing with your logo and press and email or phone number and you should be good to type it it and connect it to your iPad as well.

Do you have like service on your iPhone? And is your apple account connected to your iPad and your iPhone?