Earn 2 candies with your buddy

Walk it. Take advantage of the current event, you get lower buddy distance.
Add a pokemon as your buddy by going to your profile on the lower left and clicking on the Buddy icon.

The distance required has been cut in half

I think he means how to trigger the bug that causes you to get two candies at once instead of one. I don't think there's a reliable way to trigger it. It happens to me fairly often while using GoPlus in a building with dodgy GPS reception (to get the walk distance that way), but there doesn't seem to be any pattern to when it happens other than that.

You are dumb, it's a double candy event, when you transfer you get 2 automatically. Now is a good time to transfer your unneeded rare mons.

The question has been answered....
I'll just add some tips...
Use Gyarados or Magikarp as your buddy to obtain (2) candies as quick as you can... just for only 2km walk.... And one more thing you really need magikarp candies for special quest which requires 400 magikarp candies (evolve a magikarp)...
Good Luck Man....