All of these stores are offering digital codes that will be delivered to your email or account in a matter of minutes. One important point: as these memberships are available at a promotional price, you need to activate them on your PlayStation account before the end of the Days of Play sale on 9th June.
If you've still got a lot of subscription time in the bank you can simply stack this on top of your existing membership while it's discounted. However, if you've got more than six months left on your membership, this PS Plus deal will likely return for Black Friday so you can save your money for another time.