Each website is created differently. But most Online website editors (such as WordPress, Wix, Squarespace, etc.) make it easy to add HTML code. You will need to find the tool within your website editor that will allow you to add HTML code to your site. You can usually find an HTML editor or code block in your tools. This is usually amongst other options of items to add such as text, photographs, links, etc. Usually if you find this symbol </>, that is the tool you will need. You may click on the logo for your website builder below, that will take you to their help section.