Many times when a person starts a business it is usually just a small company owned by a solitary person (sole proprietorship) or by two or more people (a partnership). With a corporation, however it is the one seen as an individual even though it may be made of hundreds, maybe even thousands of people. This means that the corporation has its own rights and responsibilities.
To start a corporation, a form is filed, this is done by the Secretary of State in the state where the corporation is started. Like a person, it is a whole seperate entity from those who owns it, it is also responsible for all the debts that it creates. In fact, if the corporation fails and goes bankrupt, none of its stock holders will have to worry about the bank coming for their assets.
The corporation will give a piece of its ownership to anyone who invests through stock certificates which usually tell them how much of the company shares that they own. The corporation will keep a list of all the people who own it. These people may be called either stockholders or shareholders.
In most cases, the stock will have different classes, the preferred stockholder's will make a certain amount of money (cash divident), paid every year. With what is called common stockholders will need to pay their liability first. After the debt is paid if there is money left, the prefered stockholders are the ones who are paid first, then if there is anything left then common stockholders are paid.