how do i make a mac.com username?

You need to make an iCloud.com username. .mac and .me are retired, and have been replaced by iCloud as the email domain (if you previously had a .mac or .me, it still works).

HTH

History.

Originally @mac.com names were issued for trial and Paid For .Mac Accounts starting In 2002.

All Account types, Trial, Paid For or Lapsed continued as "iChat" Screen Names with the AIM Service

In 2008 Apple changed to the MobileMe service.

This meant that Trials had to be ended or you got charged.

This meant you could only use Paid For IDs as Valid AIM Screen Names.

Notes.

1) For email purposes @mac.com IDs could be linked to @me.com names.

2) Apple kept the @mac.com Registration page as an "iChat Name" page. You could still register for an @mac.com name but it only worked with the AIM service (i.e. iChat)

iCloud.

During 2011 Apple start to wind down MobileMe not accepting new registrations and Started iCloud.

In June 2012 you stopped being able to access your MobileMe account.

Initially all iCloud Account got @me.com email accounts.

In the case of existing @me.com IDs it seems they changed servers.

Later they offered @icloud.com names.

At the end of MobileMe they also ended access to the @mac.com registration page.

iCloud issued IDs (@me.com and @icloud.com) will work in iChat 6 and up.

@mac.com names will work from iChat 1 throught to Messages 8 (at time of writing the latest version) as a Valid AIM Screen name.

NOTES 2

As you could have kept an @mac.com ID "Alive" for emails across all the changes by linking them first to MobileMe and the iCloud one, they can still be used as iMessages Accounts (although in Messages 8 they do appear to have to be linked to an iCloud account).

Your ID for iMessages can be any Apple ID you have - except that in Messages 8 it does seem to have to be linked to iCloud even though after that it makes no use of iCloud (Different Servers).

i.e. it could be a Google email that you used to create an App ID or some other external to Apple email.

8:27 pm Thursday; April 17, 2014

Hi,

Some of this info is going to change by the end of June 2014.

See http://support.apple.com/kb/TS5224

This has also been appearing in my Mavericks Messages app.

It would appear at the basic level AIM are not longer willing to support the three different types of Apple Issued IDs.

However the article implies (at least in the first few lines) that moving to Messages or later version of iChat 6 (Lion) will allow the @mac.com and @me.com names to work.

The bottom of the article is about converting to AIM names or upgrading to Mavericks and seems to forget to tell you what will or will not work in Mavericks (or the other lower version in Mountain Lion and Lion that they say will work still).

I have an enquiry with the Hosts to try and clarify this.

9:48 pm Saturday; April 26, 2014