You can easily send someone your contact details either by doing it the old-fashioned way of dragging a contact card out of the Contacts app and then attaching it to an email, say, or by using the new Share commands since Yosemite, but the problem with this basic method is that you might have information on your card you don't want others to have.
For example, you might have defined a relationship with your spouse so that on your iPhone you can say "send a message to my wife" without having to specify who you mean, and you might want to keep that information private for security reasons.
Now, it's easy. In Contacts' preferences, click vCard then Enable private me card. Now, when you go to your Me card in Contacts – and you might have to define one first and click Edit, you get a series of checkboxes next to each field to show whether it would be included when you share a card.
For example, you might have defined a relationship with your spouse so that on your iPhone you can say "send a message to my wife" without having to specify who you mean, and you might want to keep that information private for security reasons.
Now, it's easy. In Contacts' preferences, click vCard then Enable private me card. Now, when you go to your Me card in Contacts – and you might have to define one first and click Edit, you get a series of checkboxes next to each field to show whether it would be included when you share a card.