Based on the research of people like Albert Roy Davis, Walter C. Rawls and many others the use of magnets has become a field of healing that should be more 'mainstream' but to this day is treated by the medical profession as' fringe quack medicine '. This subject is vast and would require an entire text to do the subject justice, however I will attempt to give you a 'taste' of what is possible when using magnets to treat the human body naturally. The therapeutic use of static magnets has gained acceptance for the treatment of a number of physiological, cardiovascular and neuro-musculoskeletal problems issues that range from pain relief to having the potential to prevent heart attacks.
The uses of unipolar and bipolar static magnets, as well as other forms of magnetic therapy's which include the highly studied pulsed electromagnetic fields (PEMF) have been researched since well before the turn of the century. Magnets have an effect on the body simply because when you think about what it is made of (mostly water and minerals), are ionic molecules (a charged atom or molecule), which means they all carry an electrical charge and have positive and negative poles . This is significant if you remember back to the days of your early childhood science experiments that used magnets to display the 'fields' they produce using iron filings. These same fields can have a direct impact on the body.
Even after all of the research that has been done using magnets, it is still not entirely clear as to how they work. It is just known that they have an effect on human physiology that has been replicated and has been shown to have an effect on the biochemical chain of events that occurs in the body. One specific effect has to do with the way minerals and even water are utilized in soft tissue after trauma and in the normal everyday biochemical processes that occur on a daily basis. [1,2] Because certain magnets have these effects on the body, they were shown in one study to delay, and in some cases dramatically reduce acute neuronal swelling after the injection of chemicals that overstimulate nerve tissue. 
The action that a magnetic field has on the body reduces the excitotoxic, hyperexcitability and the retention of fluids that occurs at the cellular level between the affected tissues due to trauma. The pain that is associated with post traumatic events such as slamming your finger in a car door is not limited to one simple chain of events. With this in mind, and understanding that magnets can regulate many systems in the body, especially after a traumatic event, they can help to prevent the biochemical cascade that occurs after the fact.
The human cell is a very complex anatomical entity that can be affected on many levels. Trauma can cause modifications in the natural movement of ion-channel proteins, it can also cause physical changes in the lipid (a type of fat) bilayer the makes up the cell wall and which inhibits the inward movement of ions and water. The good news is that if you act right away after a tragic event by placing magnets on the affected area it can have a significant clinical effect. 
Many researchers have looked at the use of static magnetic fields (SMF) in animals and in humans; in one animal study it was found that SMF's affected the magnetic fields of some internal organs of the test subject. It was also found that a magnets orientation during the treatment period could have an effect on blood chemistry as well as organ function. 
Other potential uses for magnets include their use in treating circulatory issues where the magnets were shown to reduce the thickness, viscosity and the flow of blood. An article in 'Science magazine' that was published in 2011 discusses the use of magnets for this purpose. Located at: http://news.sciencemag.org/health/2011/06/magnets-keep-blood-flowing
In doing some of my own personal research on companies that sell just magnets, I found that there are many companies that are only sellers of the actual physical magnets, and do not have any knowledge of their use in regards to what is discussed above. Then there are those who sell magnets for the therapeutic use, many of which do not have the clinical training or technical background to be able to have an educated discussion as to how they should be used responsibly. I did talk to one company owner that provided me with some insight that I could not find elsewhere. One great nugget of info that he shared with me was that most company's products are not oriented correctly. There is a difference between magnetic North and polar North; Many of the products being sold on the web are directed towards polar North. Their site also has a lot of great information on it that I also found to be very helpful www.biomagnetics.com .
Please keep in mind that there is a science to this, and as it is with the human body when it comes to healing, it is almost never a one dimensional approach. Actual healing will require a multidimensional method that may also include the use of magnets.
1. McLean M, Holcomb R, William A, Pickett J. Effects of steady magnetic fields on action potentials of sensory neurons less in vitro. Environ Med 1991; 8: 36-44.
2. McLean M, Holcomb R, William A, Pickett J, Cavopol A. Blockade of sensory neuron action potentials by a static magnetic field in the 10 mT range. Bioelectromagnetics 1995; 16: 20-32.
3. McLean M, Holcomb R, McDonald P, Sanderson L, Lombard K. A static magnetic field slows kainic acid-induced neuronal swelling. Abstracts of the 21st Annual Meeting of the Bioelectromagnetics Society, Long Beach California, p. 132.
4. Vallbona C, Hazlewood C, Jurida G. Response of pain to static magnetic fields in postpolio patients: A double blind pilot study.Arch Phys Med Rehabilitation 1997; 78; 1200-3.
5. Milovanovich I, Cirkovic S, De Luka S, Trbovich A, et. al. Homogeneous static magnetic field of different orientation induces biological changes in subacutely exposed