Depth of Field: The pictures above change the aperture setting of the camera lenses, creating a sense of depth in their images. The larger the apertures (smaller F-stop number) and closer the focusing distances, the shallower depth of field is. Other example of Shallow Depth of Field: http://digital-photography-school.com/17-beautiful-images-with-shallow-depth-of-field
If I could only teach you one thing in this photography basics series, it would be to set your camera in aperture priority for the next six months. When you want full depth-of-field, choose a high f-stop (aperture). When you want shallow depth of field, choose a lower f-stop. Your pictures will DRAMATICALLY improve when you learn to control the depth-of-field.