Dear Smith,
CEO - Top executive responsible for a firm's overall operations and performance. He or she is the leader of the firm, serves as the main link between the board of directors (the board) and the firm's various parts or levels, and is held solely responsible for the firm's success or failure. One of the major duties of a CEO is to maintain and implement corporate policy, as established by the board. Also called President or managing director, he or she may also be the chairman (or chairperson) of the board.
CHAIRMAN (CHAIRPERSON) - The chairman is the highest office of an organized group such as a board, committee, or deliberative assembly. The person holding the office is typically elected or appointed by the members of the group. The chairman presides over meetings of the assembled group and conducts its business in an orderly fashion.
The highest-ranking executive in a corporation. The chairman leads the board of directors in setting broad corporate goals and determining if managers are, in fact, pursuing and achieving those goals. In large corporations, the chairman is not ordinarily involved in day-to-day operational activities, although it is likely that he or she was the chief executive officer before attaining the position of chairman. In some corporations, the chairman also serves as the president and the chief executive officer.
MANAGING DIRECTOR - The managing director is a leadership role for an organization, and the MD may fulfill a motivational role for the workforce, in addition to an operational role in the running of the business.
Again, there are very few chances for a company to have a CEO & MD in the structure. Normally, industries will have MD on their board, and IT, ITES, Biotech, etc., will have CEOs on their board. The Chairperson would be either appointed by the board of directors or the owner/president of the company.