I haven't played with EC2 yet (but it's on my list). I know about a firefox plugin that helps manage instances (http://sourceforge.net/projects/elasticfox/).
As far as I know you launch the instance, ssh on it and have fun. That url is your instance address. You can make a loadb alancer by installing Apache or Nginx on a server (instance or other) then from there proxy to your instances (you'll have to open the ports). See the Nginx wiki for more documentation (http://wiki.codemongers.com/NginxLoadBalanceExample). If you need help configuring the Nginx shout.
It's basically VPS but where you pay by the hour and it doesn't have a static IP and persistent hdd. You can also use a AMI with what do you need (I saw there was one for Rails).