What do I have to do once my 30 day free trial is over? I don't have a product code.
Thats the reason behind software which allows you a free test drive for free for a limited trial period - you can decide to either buy the software or live without it.
In case of Prime you can still use the software after the trial period with limited functionality.
@Werner_E and how do I buy it? I'm new at this so I have no idea, and how much does it cost?
As I see it you my buy at a local dealeer or reseller or directly at PTC.
The PTC store
lists a price of USD 600,00 for the regular version and USD 60,00 for the student edition. These are only subscriptions which entitles you to use the software for just one year. This fact makes the software quite unattractive for many user as it means that you loose your intellectual property packed in the worksheets you created, as soon as you decide not to feed PTC with money annually anymore.
If you are a student, you may contact your university - they may be able to make you a more attractive offer for an academic license.
You can also decide that you don't need the programming, solve blocks and symbolics, nor the silly 3rd party graphing tool, and that you continue to use the Express version of Prime that you end up with, at no cost.
In that case you may benefit from the Express implementation of many of the functions that PTC considers Premium functions here: https://community.ptc.com/t5/PTC-Mathcad/Prime-Express-A-joke/m-p/604216