Most websites on the Internet can be accessed using both just their domain name and the www subdomain and domain name. For ex: www.example.com and example.com may lead to the same website. Some search engines consider the www version and the non-www version to be seperate websites and assign different Search Engine Results Page (SERP) positions and or page rank to them. This often results in a split page rank where the non-www and www versions of a site have different page rank. To prevent something like this from happening it helps to canonicalize your website URL. This means that you should select one version as a standard and redirect from the other to it.
domain names
How to access your website at your new web host before DNS propagates
Often when switching hosts or signing up at new host you’ll have to set your domain’s name servers to your new website host’s name servers. This step is necessary because it allows your new host’s servers to receive and serve requests for your website from your visitor’s browsers. However the Domain Name System (DNS) is such that it takes time for this new mapping between your domain name and your host’s servers to propagate across the Internet.
Depending on your new host’s DNS servers and your Internet Service Provider it can take anywhere from a few hours to a few days before you will be able to access your website via the domain name. If, in the meantime, you want to upload files to your website and test it you will need to edit your HOSTS file to manually map your domain name to your web host’s IP address.