E-commerce is can be further categorized into the following:
Business to business is one in which a company deals with another company for business and exchanging of goods, products, services. Some of the examples of b2b e-commerce sites are a company's official site, brokering sites etc.
Business to customer is one where the company sells its goods to the customer or trades with the customers. This is electronic retailing and called as e-tailing in common. One of the best examples is amazon.com.
Consumer to business is when a customer works for a certain company for business and the company buys it, here the consumer has to price the trade. Example for such a site is priceline.com
Consumer to consumer is more like auctioning, bartending, etc... where a consumer places bid and other buys it.
Here the websites acts an intermediate for the business Example for such sites is eBay.
E-Commerce provides advantages to both the Business provider, consumers. For the business it is provides easier way to market a particular product at low cost and also the product easily reaches the global market. For the consumers they can buy products from home, so no tedious work in buying and they can trade any time. E-commerce thus is a greater benefit provided it has ultimate security.