Www1 vs www2 vs www3 etc

I am trying to familiarize myself about various techniques that are used to scale websites.

I found an excellent resource from Sitepoint (http://www.sitepoint.com/article/affordable-scalable-websites) that introduces the topic to a newbie.

In the article, for one of the solutions, they mention that you can have a www.mysite.com, www2.mysite.com, www3.mysite.com. Users would then connect to any server depending on the load balancing algorithms.

My question is, does one register www.mysite.com, www2.mysite.com, www3.mysite.com? How does one direct users to each of these unique URLs (thereby directing them to a server)? Is this done by the load balancer?