Most often, the dividend comes in the form of cash - a company will pay a small percentage of its profits for each share of its stock. However, it is not unheard of for companies to pay stock dividends.
Companies are in no way obligated to pay dividends.
There are basically three dates to keep in mind when considering dividends. The second is the record date, on which the company draws a list of all current shareholders, all of whom will receive a dividend check. For practical purposes, however, this is an obsolete date. The ex-dividend date was created to allow all pending transactions to be completed before the record date. Further, for all pending transactions that have not been completed by the ex-dividend date, the exchanges automatically reduce the price of the stock by the amount of the dividend.