Many people think that the www in www.mydomain.tld (tld = top-level domain) is a part of the domain name.
This is not the case, www is the name of the computer www in the domain name mydomain.tld.
When you write www.mydomain.tld in your web browser you call for a web service on a computer connected to the Internet. It could equally well be called zzz, w3, or anything at all. The reason for naming computers with a web service to www is that this name suggests that this computer does indeed have a web service.
There is no need to include “www” in your website’s address. It was a URL prefix added in the early days of the web and caught on by accident and is fast loosing popularity.
By default a web server should show your website at both www.mydomain.tld and mydomain.tld.
The http:// is even less a part of the domain name. It stands for Hypertext Transfer Protocol and the reason for writing it is to tell the web browser to call for the web service on the computer to which you are connecting via the Internet.
Most web browsers will put http:// in front of the web address automatically if you do not type it in.