Showing Crawl errors in Google Webmaster tools?

If you have a Google account and a website you most likely added Googles "Webmaster Tools" to your account. If not, you should! It gives you great information.

Webmaster Tools is a snapshot of everything you need to know (and it's free). The information it gathers on your site is priceless.

• Top Search queries (impressions and clickthroughs)
• Links to your site (who is linking to what page)
• Keyword significance of your site
  
• Crawl errors
• Diagnostics and HTML suggestions
• You can even go to a lab to see exactly how googlebot sees your site!
• Site performance (how fast your site loads, tools to make it load faster)
• If any Malware is detected on your site
• Sitemaps can be submitted to tell Google about pages on your site they may not have discovered
  
• Subscriber stats and more!
  

What if you don't want a page/directory to be crawled and indexed? Or the page no longer exists but made it in search results and is showing "page not found" crawl errors?

Set an easy robots.txt for Googlebot. Here's a great site that can teach you more about robots.txt http://www.robotstxt.org/robotstxt.html.