How to Install the Signup Form on Shopify
Step 1: From your Shopify admin, go to Online Store > Themes. Then, click Actions > Edit code. See the Editing Theme Code guide by Shopify for complete details.
Step 2: The code editor shows a directory of theme files on the left, and a space to view and edit the files on the right. Click on the file Layout > theme.liquid.
Step 4: From your Shopify admin, go to Online Store > Pages and paste the Prefinery form code into the Page where you would like to display the Prefinery form. Alternatively, if you would like to show the Prefinery form on every page (for example, in the footer), edit your theme code and paste the HTML into the appropriate file.