I want to use Gumroad

After taking a look at their service, it looks to be just a simple service in which they handle to purchase gateway, similar to PayPal. While you cannot use this to build a website, as it is something hosted on their servers, you are able to use it for the purchase of individual products. On their documentation, I have located an article that will allow you to embed product links hosted with them on any page: Gumroad overlay