Firstly let us explain 404 errors, this doesn't mean that you have a total of four hundred and four errors on your website :) a 404 or Not Found error message is a standard HTTP response code that is sent from the server when the requested item couldn't be found. This could be an image, file or web page that has either been removed or the visitor has mispelt the required item in the URL, or it could be that an inbound link to your website has been incorrectly linked.
404 errors are more common if you have moved your website from an alternatively hosted server to Superia, most of your URL's would probably have changed so if somebody has bookmarked one of your old URLs then they would recieve a 404 error when trying to view it.
You can edit the 404 error page in the system by going to Content > Pages and then editing the Customer 404 error page.
You might also recieve 404 errors for pages that have never existed and sometimes don't make sense, these are probably generated by online bots or scanners trying to crawl your site to find certain pages. Sometimes these bots have negative intentions and are trying to find back doors into your website, however there is adequate security in place to stop this from happening. If you mark these 404 errors to be ignored then they will be removed from the list and you will not be notified of an attempt to access that URL again.
You can create redirects for 404 errors to pages that you actually want people to be able to find, to do this you can click on the redirect link next to the 404 error and you can then enter the correct URL that you want people to see when they visit the incorrect URL again in the future, this will cause them to bypass the 404 error and go straight to your preferred page.