If your site involves payments of any kind, you will need to deal with PCI compliance. That’s a bunch of requirements that your bank will make you meet. I am a specialist in PCI compliance issues. I’ve even taken older sites that failed their PCI scans, and I’ve reworked them so that they can pass. I can explain all of the technical parts of the requirements in plain English.
You will need to understand another set of technical details if your site is going to have high traffic (thousands of people at a time).
How the site is backed up, how to change the text and photographs, how it is protected against attack, how it is secured–all these involve some technical know how. You can either learn that or pay someone to deal with it for you.
If your site does not involve money or thousands of people at one time, then you don’t have much you need to know.
If you hire me to make your site, I’ll explain what you need to know up until the contract is fulfilled. If you hire me to maintain your site, you can ask me to explain things as they come up.