How are you processing the orders??
You either need a third-party shopping cart
A new hosting package that supports a server-side language...then of course you'd have to learn a server-side language (PHP, ASP, ColdFusion), or pay someone to create it, or find a script and learn how to implement it
You can find a hosting company that includes an e-commerce system
Your choice really depends on the knowledge you already have, the money you're willing to spend, and your willingness to learn