What is TMJ and what can I do to fix it?

Joint pain. Tmj stands for temporal mandibular joint which is the joint between the upper and lower jaws. Therapy usually starts with having an occlusal appliance(night guard) made. Wearing the appliance helps to relax the muscles surrounding the joint and helps to alleviate pain. A dentist should be consulted to determine the cause of your problem.
A few ideas. Depends on symptoms, and cause of symptoms. 3 signs of TMJ dysfunction: joint noises, joint pain & limited oral opening. Self treat with soft diet, jaw exercises, massage, heat/cold, OTC pain meds. A splint or physical therapy would be next. Occasionally muscle relaxants, biofeedback. Xrays are done for diagnosis. Surgery usually reserved for serious symptoms not responsive to other treatments.
Evaluation Needed. At home you can do otc anti-inflammatories such as Ibuprofen or advil (ibuprofen). Soft diet and physical therapy are also some things you can do at home. Heating pad or ice is also options. You should go to the doctors to get evaluated and get a definitive diagnosis and treatment plan.
TMJ treatment. Temporo-mandibular disorder is the second most frequent cause of orofacial pain after dental pain. Proper diagnosis is the key to the successful treatment. See an orofacial pain practitioner for a consultation and management. They are the expert in TMJ nonsurgical, conservative, predictable and effective treatment.
Stability / function. A TMJ problem exists when the bite, joint, muscle function and head and neck relationships are compromised. Use a reversible diagnostic phase (splint and physical therapy) to find a stable position. Then consider the best options that are possible to maintain the stable position as the bite is approximated to a stable joint and muscle relationship.