Using depth of field:                                                        Back
Depth of field is the depth or distance from focal point that things remain in focus. It is controlled by the aperture. You can use this to your advantage: By throwing the fore & backgrounds out of focus you emphasize your main subject. (F stop =  Diameter of lens opening, The lower the number the larger the opening, the less depth of field.)   See examples below.

Notice how the sharper image stands out against the blurred background. In photo of girl I also used a darker background. You would do just the opposite if you wanted everything in focus. Remember by opening and/or closing the lens your letting more/less light reach the film & will have to compensate be using a slower/faster shutter speed. practice at home, you should be comfortable with your camera before you need it on a trip.