A domain is similar to an address by which a visitor can locate your website on the internet. Once you have registered a particular domain name for your website no other company can use your domain name for their website. It gives your website a unique identity, therefore it is necessary to obtain a domain name for your website.
Yes certainly you can acquire a domain name for your website even before you have published your website. You can simply reserve a domain name for your website and when you are ready to publish your website online you can simply use the reserved domain name for your website.
After the registration process for a domain name is completed you can no longer change your domain name.
Yes you can register multiple domain names depending on their availability. You can register more than one domain name and the process remains the same.
After the registration of your domain name if you wish to modify your domain name you can do so by simply accessing managed domain options.
There is a possibility that someone else applies for the same domain name and acquires it prior to you getting it. You can improve your chances of getting a domain name by using a domain name that is simple and unique.
An email will be sent to you as a confirmation of the same. It is advised to make a print out of the same to use in the future.
Once the registration process has been completed you will have to register a new domain name if you don't wish to use your existing domain name.
DNS also referred to as nameservers consist of information related to your domain name. When a user types in your domain name on the browser, then the browser uses that DNS to locate the IP address of the server associated with your domain name.
A subdomain is to guide your visitors to a specific section of your website such as mail.ewebguru.com is the sub division of ewebguru.com.