If you have broken internal links then fix them. If you have broken links from external websites, setup redirects if from non-spammy source(s).

Hey there!

You can't fix that on Webmaster Tools. You have to fix them in your site first and then recrawl them on Webmaster Tools. First check if those are really 404 pages, sometimes it is a momentary glitch of your hosting. If this happens to often you may need to think moving from your current hosting provider. If you changed the URL of a page, you would need to write a 301 redirect from the old url to the new one in your htaccess file.

By the way, I hope you have a custom 404 page that doesn't get people out of your site!

Fix all your broken URLs and redirect 301 to the new URLs.

Only being that said noone can give you a proper answer. You need to tell us more, is this a blog, or a website written for example in PHP, are other pages working......

use 301 redirect

Webmaster Tools isn't hosting your site so it's not going to fix a 404. If a URL is broken, fix it at the host/site.

Before you go hog wild on 301 redirects, figure out why you have a 404 in the first place, 301 redirects are band-aids.

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Webmaster Tool can only show the URL's of the pages that have 404 error. But, it will not resolve your errors. You have to fix all the broken links on your website. If you have changed the URL of any page then, redirect the old page to the new one using 301 redirect.

Often times the 404 Not Found error appears because the URL was typed wrong or the link that was clicked on points to the wrong URL. but there is another issue with that when some link broken from external resources that has been used for optimizing website than 404 error showing and some of website owner customizing this error. so there is a lot of issues when 404 error coming.