To get a .com or .net domain you need to purchase it. There are no free sites unless the host of the site, wishes for you to share it with him or her.
You can use
DynDNS to setup a free self hosted account. Your free domain and you self host. The domain will not be .com or .net but there is a selection to choose from.
You can also get a free .tk domain but hosting needs to be payed for.
I hope that helps, if not, feel free to ask
