Paid for WordPress website but it doesn’t work

I paid someone to build me a website and they used WordPress (which is fine), but I have no idea what I’m doing with it and I keep getting website not found when I am trying to work on issues.

I have loaded my inventory but when customers have tried to purchase they get a ‘500’ site not available error.

I would either like to learn to how fix or pay someone to fix my website.

The page I need help with: [log in to see the link]