My iphone xr came with 128 GB of data however now it’s telling me my storage is full with 5 out of 5 GB

That's only iCloud storage for various storage and backups on Apple's servers. The default is 5 GB with any Apple ID account. I believe the cheapest paid storage is 50 GB.

If you don't have much, it will primarily save your settings on iCloud.

To see your device storage, it's Settings > General > iPhone Storage. There's also Settings > General > Capacity/Available. In addition you can connect to iTunes and get a representation of storage used/available. This number may not match though. The number on the phone is supposed to be the most accurate.

For the love of G** spend the money ( $1 US a month) for 50 GB and start automatic backups today. Automatic iCloud backups have saved millions of people from losing ALL the files on their devices.

It's a trivial amount of money spent that will give you enormous benefits later on.