Depth of field is the area of an image that is in focus, for example, if you focus on something 6 feet away, you may find that everything 1 foot beyond that and 2 feet before is in focus, but everything else is blurred. However the depth of this area that is in focus, can be adjusted by the aperture of the lens as well as the focal length of a lens.
Wide angle lenses give far deeper Depth of Field and telephoto lenses give far shallower Depth of Field. That is why Landscape photographers frequently use wide angle lenses closed down as much as possible to get everything in focus, yet portrait photographers use telephoto lenses open as much as possible to get a shallow Depth of Field, to blur the background making the subject stand out (called subject separation)
Understanding how Depth of Field works will improve your photography dramatically, so it is definitely worth experimenting to learn and understand.