No blank spaces. Domain Names are case insensitive, ie. Many large companies, particularly in the communications and entertainment industries hold domain registrations for many names covering various trademarks, trade names, or simply variants on their company names. In the past, companies were discouraged from registering more than one domain name. Now, however, domain authorities have bowed to the demands of Internet users and are willing to register as many domain names as you need.
Computers identify each other with numbers rather than words.
DNS has servers located all over the Internet which perform the translation between names and numbers for other computers.