How do I buy a new Straight Talk phone?

It's a dumb question, but I have never bought a phone before so the whole process confuses me. My parents got me an iPhone 5s with Straight Talk a couple years back. I'm looking to upgrade to a Moto G7 with Straight Talk. How do I do this? I would like to keep my number.

When you upgrade, as long as your new phone will be acceptable to your cell phone company who provides you with your telephoning service and wireless connection, you will be able to use that new phone without changing cell phone companies, and keep your same phone number. Even if you switch to another company, many of them will be able to offer you service keeping your same number, but not all of them can do that.

Just go to Walmart and pick out the G7 and pay for it.