Almost anything can be used as a frame for your subject, including people!
Context is another advantage to framing. Shooting through a window, using an archway, or framing with trees gives the viewer a sense of where the subject is in the photo.
Be careful when using frames, however. If done wrong, a frame can distract a photo. Keep your focus on your subject, and your frame relevant to your shot. Also make sure that your frame does not obstruct too much of your photo or subject.
There you have it! An easy way of adding interest and focus to your composition!