eCommerce provides the capability for your customers to shop online.
A full eCommerce implementation is more than just a shopping cart.
For the end user it consists of a product catalogue, shopping cart, checkout and payment facilities, and possibly recommendations and related products.
The store owner has the tools to manage the store: orders, customers, products, attributes, reports and a whole host of store configuration options.
Bobbing Wide currently use Ubercart to implement eCommerce sites. We will only install and configure Ubercart if you need it. You will have to make a lot of decisions about how to present your product catalog, take payment, charge for shipping, handle discounts, etcetera.
If your site is only going to use a Third party credit/debt card payment solution (such as PayPal) then you may not need http security and security certificates, nor may you need to have standalone hosting.
The Ubercart eCommerce solution for Drupal comes with a whole host of modules. There are also quite a few contributed modules for different payment gateways and payment options. Note: Ubercart is dependent upon Drupal. For WordPress there is an eCommerce plugin, but Bobbing Wide do not have experience of this, yet.