Visitors may enter the United States on a B-1/B-2 visitor visa. B-1 is for visitor – business and B-2 is for visitor – pleasure. These visas must be applied for while the applicants are in their home country and have an interview at the consulate. In order to apply for a B-1/B-2 Visa, one must complete an electronic DS-160. Learn more about the DS-160 here or check current visa wait times here.
If you fail to leave after the time given on the visa, you will be overstaying your visa and violating US immigration law. If you overstay your visa for 6 months up to one year, then you will be barred from the US for at least 3 years upon your departure from the US. If you overstay your visa for one year or more, you will be barred from the US for at least 10 years, again upon your departure from the US. Exceptions and waivers exists for people who overstay their visa; therefore, it is best to consult with an immigration attorney as soon as you realize you overstayed your visa -or- anytime you plan to leave the United States after overstaying a visa.