Framing your photograph can turn what would otherwise be a boring picture into a visually pleasing one. Often times an element in the foreground can be used to create the frame. Some examples of framing include using an overhanging tree branch, a window frame, a door, arches, a fence, rows of trees, etc.
A frame serves to isolate your main subject and create an interesting composition. Oftentimes, it's the feeling of depth you're after. You may choose to keep the detail of the frame (as in a wall, fence or branch), or let the frame go completely dark (as in a window frame).
When you are composing a shot, keep your eyes open to foreground (and sometimes, even middle or background) objects that can be used as a natural frame. You may need to physically back up a bit, kneel down for a more pleasant composition, or zoom in to include your subject within your chosen frame.
Image editing software can also be used to create framing effects after the fact by combining two or more pictures. You can create some very dramatic effects this way and the joy of it is, you are truly only limited by your imagination.
A word of caution is necessary here, however. While there is nothing wrong with combining different images to create a separate one, please be very careful about employing artificial frames on identifiable scenes and landscapes.
As an extreme example, don't frame the Statue of Liberty by the St. Louis Arch. Unless your purpose is to create dissonance within your viewers' minds, that picture will just look strange.
So, the next time you are ready to take your shot, look around and see if there is an object nearby that you can use as a natural frame. I recommend that you try to take a picture without the frame, and another one with the frame, and then compare the two. Chances are, you will like the one with the frame better!