There are many possibilities of Ecommerce site. If your ecommerce site get proper exposure then you will have a chance to get customers from all over the world. To deliver products you have to have a store of product to the specific place. You have deal with the supplier of the product that you will get customer through your ecommerce site make a handsome share of profit. Payment of the ecommerce transaction usually performed through merchant account there may have alternative depending on your product and services.
There are a bunch of low end ecommerce solutions provider, only a handful of high end ones. Really depends on what you are looking for and your budget