The Status of an Opportunity record reflects the Status of the Customer associated to an opportunity record. With that being said, creation of Opportunity status can be done by creating a Customer Status since it will also be available as an Opportunity Status. Please take note that only Customer Statuses that are on Prospect and Customer Stage will appear on the Opportunity Status dropdown list.
The creation of a Customer Status can be found in:
Marketing, Sales Force Automation, and Partners : Sales Force Automation : Setting Up SFA : Customer Statuses
Customer Statuses | Answer Id: 9769