In the figure above, the first two channels are "indirect-marketing channels".
Channel 1 contains two intermediary levels - a wholesaler and a retailer. A wholesaler typically buys and stores large quantities of several producers’ goods and then breaks into the bulk deliveries to supply retailers with smaller quantities. For small retailers with limited order quantities, the use of wholesalers makes economic sense. This arrangement tends to work best where the retail channel is fragmented - i.e. not dominated by a small number of large, powerful retailers who have an incentive to cut out the wholesaler. A good example of this channel arrangement in the UK is the distribution of drugs.
Channel 2 contains one intermediary. In consumer markets, this is typically a retailer. The consumer electrical goods market in the UK is typical of this arrangement whereby producers such as Sony, Panasonic, Canon etc. sell their goods directly to large retailers and e-tailers such as Comet, Tesco and Amazon which then sell onto the final consumers.
Channel 3 is called a "direct-marketing" channel, since it has no intermediary levels. In this case the manufacturer sells directly to customers. An example of a direct marketing channel would be a factory outlet store. Many holiday companies also market direct to consumers, bypassing a traditional retail intermediary - the travel agent.