You are not dumb, you are just a newbie. don’t worry.
Generally, Main tag is not necessary for loading the webpage, but we better consider it while coding.
Take a look at the w3schools description:
The <main> tag specifies the main content of a document.
The content inside the <main> element should be unique to the document. It should not contain any content that is repeated across documents such as sidebars, navigation links, copyright information, site logos, and search forms.
So its more useful for search engine while crawling your website, they will understand that OK it’s your main part, this is the article part this is the header, etc. On the other hand, it’s good for yourself too, you can organize your codes better. Keep in mind, the more standard you code the more professional you become.