Usually a person or company with access to the internet.
The Internet
That may sound obvious but without it the customer takes a trip to the shops.
Web Site Host
The trader/company selling it's goods or services must also have access to the internet. This is normally achieved via a web site host (see Web Site Hosts menu item)
Database
of company products and services. The trader should provide this as the customer will want to know what products the trader offers.
Method of payment
A method for the customer to make payment for their required goods and services. This may be done electronically or in a more traditional method. (see The Money Side of e-Commerce menu item.)
Distribution
The trader/company must provide an avenue for the goods and services to be despacted to the customer. Either via postal delivery, courier or electronically.