Well, the idea can simply be explained as blurring everything except for the focus area. If you look at all of the above pictures, the outer extremities are blurry in comparison to the focus point.

When I do them, I create a duplicate image over the actual image, and then do a guassian blurr on the bottom, original picture. Then on the second layer, create a layer mask and use a large, soft brush to leave only your focus area left on that layer. (My favorite way to do them)

You can also use quickmask if you're familiar. But really, as with literally anything in photoshop, there are several ways you can achieve the effect. I just use the above mentioned one because its very customizable, thanks to the layer mask.

Heres a good tutorial for the tilt shift effect using quick mask for the main blurring process.

But you could probably just search for tilt shift tutorials in google and find a million of em. The effect is very popular.