The only valid characters for a domain name are letters, numbers and a hyphen (-). Other special characters like the underscore (_) or an exclamation mark (!) are NOT permitted.
Example: your name.com (not correct, no spaces allowed)
Example: your-name.com (is correct)
A domain name can be up to 64 characters long -- including the 4 characters used to identify the Top Level Domain (.net, .com, .org or .edu). Do not type the www. before your domain name when registering.