Administration and overhead roles

The main roles in the company administration are the "CxOs" - the Chief Something Officers:

• CEO - The Chief Executive Officer is the person given the task of fulfilling the tactics and strategy of the company as decided by the Board of Directors.  
• CFO - The Chief Financial Officer is responsible for managing the money, which includes setting revenue targets, controlling expenses, and raising cash if necessary.  In some organizations, the CFO is also responsible for the day to day operations, but in others that is the duty of the COO.
• COO - If the company has a Chief Operations Officer, then the CEO is likely to play more of a strategic role while the tactics of making the company run on a day to day basis are handled by the COO.
• CIO - The Chief Information Officer is usually a highly operational (meaning dealing with the tactics and implementation) of the technology infrastructure, especially computers, phones, databases and other specialized information systems.
• CTO - Companies which are technology-based (like software or computer hardware manufacturers) may have a Chief Technology Officer who is responsible for the strategic (long term) selection of technologies, both for internal use and in the company's products.  If there is no CTO, these functions can be performed by the CIO.
• CMO - The Chief Marketing Officer is responsible for making sure that the company's products are designed and produced to fit the needs of the clients, and with a set of features and a price which differentiate the products from the competition.
•  CSO - In a biotech, pharmaceutical or otherwise science-based firm, there will usually be a Chief Science Officer who is responsible for making decisions about the direction of research and product development, serving a role similar to the CTO in a technology firm. 
• CPO/HR - Some companies call their Human Resources Director the 'Chief People Officer'.  HR is responsible for managing the hiring and firing process, selecting and delivering the benefits packages, orientation programs, employee education programs, and complying with the thousands of federal and state laws regarding employees.