How do ebay sellers/small online businesses ship their products cost effectively to their customers?

Everytime they get a sale do they drive to their nearest depot and sent if off? Or do they have a courier delivery service? I want to start an online shop but I find courier services charge around £6 per parcel and I can't be going to the mail depot every time I get a sale on my online store. How do these small businesses and eBay sellers ship their products to multiple addresss? & what delivery methods do they use? Regards, JMG