how to put functionality to allow other sites to import our sites users?

Question

how to put functionality to allow other sites to import our sites users?

Answer 1

Please try adding more detail to your question, but as far as I can understand you may be interested in OpenID. Read these two links to find out if it is what you are interested in.

http://openid.net/

http://en.wikipedia.org/wiki/OpenID

Answer 2

You need to create a web service of some kind. Whether it be an XML feed, RSS feed, or even (as jball mentioned) providing direct password-authenticated read access directly to your database server (mysql or mssql for example).

an example might be, if another site wants to get a list of usernames starting with the letter "u", they might fetch the data from a call something like this:

http://www.yourwebsite.com/getUsernames.php?startingLetter=u

and the returned data would be something like..

...
<user>Uncle Jim</user>
<user>UnderpantsMcGoo</user>
<user>Unstoppable</user>
...

Whichever method you choose, make sure you read up on how to get a PHP page to properly generate the desired data in the correct format.