How do I get the html code of a form I created?

If you would like to embed your form on a web page, then you can check the embed codes found under the "Publish" wizard. Here's a guide that you can refer to: https://www.jotform.com/help/34-Adding-a-form-to-a-web-page 

If you would like to actually get the form's full source code, then here's a guide that you can follow: https://www.jotform.com/help/104-How-to-get-the-Full-Source-Code-of-your-Form 

I hope that helps.