said 4 months ago:
Hi Ian, I’ve created a few sub-domains and believe the sub domain and your website are 2 separate entities.
And yes, the sub domain is crawled by the search engines just as your website would be, but they are not indexed by the search engines as the same.
You may even consider a sub folder instead of a sub domain.
Sub folder… yourwebsiteurl.com/blog
Sub domain… blog.yourwebsiteurl.com
Here’s a good article to read… http://www.seomoz.org/blog/understanding-root-domains-subdomains-vs-subfolders-microsites
It’s a good idea if you have a website that you want to keep, and have excessive content. (You can also move all the content, and domain, from the website over to a blog, so you only have one entity, but the added benefit of the blog content)
You can probably go to youtube and find a tutorial on how to set up a sub domain.
Hope this helps!