The most concise description of a 404 error is that your browser cannot find the page URL you have entered.
404 error causes
The most common cause for a 404 error is the page has been taken down or moved to a new URL – it is simply a dead link. But other circumstances could lead to 404 errors, as well. The URL of the link you are trying to view may be wrong, the server the site runs on is down, or there are connection problems.
Fix a 404 error on my site
If you see this error on your site, it is most likely that you've moved or deleted something and did not update the internal linking structure of your site. To fix the 404 errors, you can redirect the broken link to point the visitor or search engine to the correct page of your choice.
In many cases, a separate site that links to your site is using an incorrect URL. For example, if the page URL of your site is yoursite.com/wit and the other website tries to link to you using yoursite.com/wiy, it will result in a 404 error. You can try to contact the site to get it fixed, but it is a good practice to set up a redirect that points the external URL of yoursite.com/wiy to your site's URL of yoursite.com/wit.
Find 404 pages on my site
You can find 404 errors on your site by using Google Webmaster Tools, clicking the Diagnostics link, and clicking on the Crawl Errors. Clicking on 'not found' presents a complete list of all the 404s on your site. You can click on one of the items in the list that shows you all places linking to that page.
You can redirect 404 pages with the .htaccess file in your site's root folder using your cPanel's File Manager. Note: Enable the view hidden files option to find it. You can redirect specific pages or all the pages that have a 404 error. Be extremely careful when editing this file, though, as one typo can mess up your site.
To redirect a single page to another page, add this line to your .htaccess file:
If you have 404 pages, you visitors to all of those pages to your front page. If this is the case, add this line to your .htaccess file:
ErrorDocument 404 http://YOURURL
Note: If you downloaded the .htaccess file to edit it, or you're creating one for the first time, make sure you upload it in ASCII mode. Name the file htaccess.txt and change its name to just .htaccess once it's uploaded to your server.
Plugins to fix 404 errors in WordPress
If you're using WordPress, several free plugins help you manage your 404 pages and create redirects. Here are just a few of them: