What programming language(s) / skill(s) do I need to provide secure digital

What programming language(s) / skill(s) do I need to provide secure digital downloads. This means the download will occur after payment using paypal. I own a domain and use basic html. Can some computer professional advice me. Please do not give the sort of advice you normally give saying it is too difficult to learn. If I believed that I’d have trotted off to the citizens advice to get a leaflet. Please can you answer the question