If you have built a website using a free site-builder like Wix or Weebly, you will be asked to connect your site to your domain by setting an A-record or C-name.
This is done by following the instructions about setting up DNS which can be found in the following article: How do I manage advanced DNS?
However, you may find that if you have done this, you still get an error message when you enter the domain name into a browser. If this is the case, try pasting in the IP address and hitting enter. You may find that instead of a generic 404 site not found message, you see an error message from the site builder advising you that the site has not yet been published.
If this is the case, it's because your website is still in preview mode and can only be viewed if you are logged into your account. You will need to find the publish button in your account and make it live before it can be viewed.