basicly……………..
In a normal lense everything X feet away from you is in focus.
In a tilt shift lense the plane of fiocus can be wherever you want it to be, usualy at an angle either horisontaly or verticaly.
The reason it looks like a model is that closeup photography results in a really narrow depth of field (distance within which stuff is in focus) so real life can be made to mimic this effect by creating a plane of focus that intersects with the subject at an unusual angle.
Alternatively you can do it in photoshop by bluring the top and bottom of the picture, for a really bad exmple of this look at dirts photo of the Fort William finish area this month, call me cycical but look at the big screen, the plane of focus somehow manages to cut through it perfectly horisontaly, either that or they’ve just tried to make a boring photo ‘interesting’.