How do they treat oral cancer?

Multiple options. Depending on the stage and primary site of the cancer, surgery radiation and chemotherapy all have potential roles in treateing oral cancer.
Many ways. Local disease is treated by surgery and radiation. Surgery is more common. Chemotherapy, like Cisplatin and 5-fluorouracil used before or during radiation is just as good as surgery and radiation in locally advanced disease. Recurrent or metastatic disease is treated palliatively with Cisplatin and 5-fluorouracil or paclitaxil. Patients with localized disease can have 75% 5 year survival.