Google can't find my landing page, says it's 404, not found.

I am not sure if this is the right sub to post this, if so, please direct me to the correct sub. I am the sole owner and operator of a micro service business and I have made my own websites in the past, but now I have a new site and google can't find a key landing page, says it's 404 not found, but the page is right there on the website for the whole world to see. How do I correct this?