HT5441 says "If you are an existing iCloud Mail user with an @mac.com or @me.com email address, Apple has reserved an @icloud.com email address for you", so how do I claim my @icloud.com equivalent email address?

It is probably already linked to your current account and can be used interchangeably with your @me or @mac address. If your iCloud ID was myname@me.com, for example, you probably already have and address called myname@icloud.com. You can check by going to icloud.com, launching Mail, clicking on the gear-shaped icon on the upper right and selecting Preferences, go to Accounts then look under Email Addresses to see if your @icloud.com email address is listed.