Question About The Numb Song

[JuNiPER]

I noticed it's available to buy or to pre-order in iTunes for the Deluxe version but can you buy the song off the album even though it hasn't been released yet?, if not what about when it comes out ?

[JuNiPER]

I dunno. If you can buy it, doesn't that mean you get the song instantly?

I didn't know you could pre-order songs (if you don't get it right away).

How do you pre-order songs?