19 characters without including the subdomain. For example: my-domain.com.ar consists of 9 characters.
Can it include characters like accents, unusual letters, spaces, etc?
No, the only valid characters for a domain name are letters, numbers and the hyphen "-".
Is "http://www." part of the domain name?
No, "http://www.my-domain.com.ar" is a URL (Uniform Resource Locator) used by navigators to locate documents and resources in the net. It is not a part of the domain name, and must not be used on any form that requires entering a name.