Welcome to OBi-land!
First, a basic concept: number porting is a FCC-regulated process, which all carriers must follow. It uses a central, nationwide administrator, NPAC, which acts as the source of all ported number call routing. When you port a number, there are two carriers involved: a "losing" carrier (the phone company that supplies the number's telephone service today), and a "gaining" carrier (the service provider you want to take over providing service on this number).
When you port a number, you are giving the gaining carrier permission to act as your agent. The gaining carrier asks the losing carrier to take control of call routing for the number. If you've provided the gaining carrier the correct/valid account credentials (account number and password or PIN), (and, in some cases, told the losing carrier to unlock your number for porting out), then the losing carrier will agree. At that point, the gaining carrier does the remainder of the work, with NPAC.
You said you have an "old Tracfone". What actually matters is that you need to have mobile telephone
service, not what kind of handset. When you port a landline number out, you will need to pay a mobile carrier for active/working telephone service, on which to host the ported-in number. That means, you will need to (re)activate service on that Tracfone, if possible, or otherwise, you'll have to buy or borrow a different handset, if they can't activate the old one. If you need to start over with a new phone, I suggest instead using AT&T Prepaid or T-Mobile prepaid, which have better expertise at land line porting.
Rather than re-type all the details, you can read one of my answers to the question, here:
https://support.google.com/voice/thread/2559768?msgid=2571630Not all phone numbers can be ported into Google Voice.