Depth of field is one of the most important elements to consider when composing and taking a photograph. If you get the depth of field right then you can lead the viewer in to your photograph and help them understand what you are trying to portray.
Mike Browne of Mike Browne Photography describes depth of field as "like a block of sharpness which extends into your photo. You might need a big deep depth of field for something like a landscape, or maybe a small shallow one for a portrait with a soft fuzzy background".
You can choose how much sharpness you want in your photography and where you want that sharpness to be within your image.
For example, in the photograph below I have chosen a shallow (or narrow) depth of field to focus on the tip of the pencils which highlights the texture of the wood the colour of the pencils and the texture of surface they are on.
In the next photograph I am focussing on the pencil ends and there appears to be no texture in the image resulting in a less interesting photograph.
In the following photograph I am focussing the viewers attention on the text of pencil placed horizontally and both the foreground and the background are in soft focus.
In the final photograph much more of the pencil is in focus and this therefore demonstrates a wider (or deeper) depth of field.
You can use depth of field when photographing any subject matter in order to convey your message effectively.
The key aspects to controlling depth of field are aperture, focal length and focal distance.
Mike Browne is an excellent photographer and has hundreds of fantastic free video tutorials that are well worth a watch if you want to understand the tricky subject of depth of field, click on the link below to view.
Video Tutorial - Mike Browne Depth of Field