There are many different levels of producer, but basically they are in charge of procuring and organizing the materials and talent for a production (be it a play, movie, or record) from start to finish.
A producer is the manufacturer or assembler of a certain product. It's the person or entity that originates the product, which is obtained by transforming some raw materials or that assembles some parts, incorporating a new and original technology to obtain a complex product.
A producer produces products for companies. The products are then distributed to retailers or whoever the company is and where they are located. Producers may be revolved around the designing process, or they just follow guidelines that the buyer has given to them. This is an important part of the marketing cycle because they must produce the right product.