Every IRA is owned by only one person, there is no such thing as a "spousal IRA".
So you need an IRA in the name of John Smith and a separate IRA in the name of Mary Smith.
Normally, you can only contribute to an IRA if you have compensation from working (mostly W-2 income or net income from a schedule C business, but there are a few other items). The spousal IRA rules allow Mary to contribute up to $6000 to her IRA even if she does not have compensation, because she can use her spouse's compensation instead.
The maximum total IRA contribution is $6000 per person (under age 50), but you can't contribute more than your compensation from working. So for example, if your compensation from working was $10,000 and you contributed $6000 to your IRA, your spouse's maximum spousal IRA contribution would be $4000.
