Advertisement is a form of communication. It means that it is a two way process that ensures the transformation of the message to the public. In advertisement, there is a proper message that carries information what you want to convey.
Advertisement will become only two way process when it gives some response to the company back. that response will only from the relevant people and that are you target market. Generally advertisement is for all people but the purpose of it is to alert the only people those need your product.
Advertisement must carries some information that you want to transfer to your target audience. Information could be the demonstration of your product, service or any thing that you are going to sell in the market. Some time information can be social message.
Paid for means that advertisement has some cost that initially company bears then customers. Now business tycoon allocating high volume of budget just for advertisement. But it not means that they put all those cost from his pocket but finally customers pay all that cost.
Advertisement is persuasive in nature. It means that advertisement try to persuade people to buy product either by product characteristics or by some promotional efforts.
Social media is another source of advertising.