There are a number of different ways that you can get an ecommerce store set up. One there are options like yahoo stores that charge you a monthly fee and then provide a store front that you can just drop all of your stuff into and start selling things. Option 2, is using a shopping cart supplied through a web host or installing one yourself. There are a number of both open source and paid carts out there for you to choose from. Some of the open source carts include osCommerce and Zen Cart both of these carts you can find a number of templates that have been designed for them out there. If you set it up yourself you still have to deal with getting the cart installed. Setting up the template. Installing the SSL, etc. The third option is going with more of a turnkey e-commerce site provider. These will be a little more expensive than you average host but they will help you get everything set up templates installed, SSL installed etc.
Hope this helps,