A businessperson (also businessman or businesswoman) is someone who works at a job that focuses on making money. Very broadly it can mean anyone who works in industry or commerce. More narrowly, it is someone who works in the management (at high level, when the term is used even more narrowly) of a company. Sometimes the word means an entrepreneur or a merchant.
Many businessmen wear standard business clothes: a suit with collar, shirt, and necktie. However, this depends on the company, the local culture, and the country. In more informal places, neckties need not be worn.