Advertisements are the business of drawing public attention to goods and services, performed through a variety of media. It is an important part of a overall promotional strategy. Other components of the promotional mix include publicity, public relations, personal selling, and sales promotion.
Why
The purpose of advertising is to convince customers that a company's services or products are the best, enhance the image of the company, point out and create a need for products or services, demonstrate new uses for established products, announce new products and programs, reinforce the salespeople's individual messages, draw customers to the business, and to hold existing customers.
How
Advertising is how a company encourages people to buy their products, services or ideas. An advertisement (or "ad" for short) is anything that draws good attention towards these things. It is usually designed by an identified sponsor, and performed through a variety of media. Ads appear on television, as well as radio, newspapers, magazines and as billboards in streets and cities. They try to get people to buy their products, by showing them the good rather than bad of their products.