• - uCoz requires no payment;
  
• - uCoz gives possibility of full domain management (creation of subdomains, e-mail accounts etc.);
  
• - e-mail accounts are created by means of GMail service;
  
• - domain of the second level may be bought at any registrar (e.g. GoDaddy.com);
  
• - you’ll be able to register in catalogs, which prohibit registration of free sites;
  
• - you’ll be able to enter a serious banner exchange network (or advertising company), where only paid domains are allowed;
  
• - with such a subdomain Users will never loose you, even if you change your hosting (e.g. for other server Sх), the address will remain the same.
  
• - with such a domain search engines will place you higher in request lists;
  
• - one will hardly guess that you have your site in uCoz system. Thus, you will get all uCoz technologies, and others will think that you are a serious web-master.
  

Question-answer

No, you cannot.

Yes, you can. Through the control panel of the site, to which domen.net is attached, add the necessary subdomain, e.g. forum.domen.net, by specifying for it the IP address of the server, where the new site is registered. Then attach forum.domen.net in the control panel of the new site by the third method.

As a rule, it means that you should wait. If nothing has changed in a day, then there is some mistake in settings.

One site can have only one domain attached. You should either detach the first one and attach the second, then you can place other content on www.site.net, or create a new site, where the primary site will be www.site.net, and the secondary one - forum.site.net. In this case, databases (of users) will be separate, but they can be merged if both sites are on the same server.

If a domain has been transferred to uCoz servers, then there are links for editing domain records in "Domain transfer" section.

We do not offer such service.

In terms of transfer by DNS change there is a limitation, that the main subdomain and "www" subdomain will be strictly directed to that uCoz server, where the account belongs. Thus, if you parked the domain at uCoz, you cannot direct the specified 2 subdomains (empty and www) to another hosting.

It means that your domain is parked at uCoz, which is incorrect if the domain is not hosted at uCoz. Cancel parking.

It is not possible to direct several domains to one account, if this is what you mean.

The system explains the error... get to CP of your domain and configure your domain as described in ucoz CP.

No, once you have chosen the domain name you cannot change it, you can only create a new account.

The system gives you the answer: You must change the name servers at the control panel of your domain registrar.

When you use the 2nd method your new domain is hosted at uCoz servers. If you use the 3rd method - you just change the domain name (to be more precise you just get one more name for your site because it will be accessible by both names - the new one and the old one) but your domain remains hosted at another registrar's servers. So the difference is in the place where your new domain is hosted - either at uCoz or not.