Once you've enabled the required modules needed to run ubercart, as well as the modules you think you might need for your individual project-- you're not finished! There's still plenty of work to configure and customize your site. Keep in mind that your business model might require additional functionality that Ubercart doesn't include out of the box (e.g. you're a music store that sells CDs as well as music downloads, or you're a European based business that needs a VAT calculated for products sold). For additional functionality, visit our contributions section to see if there are any additional modules you might need. If you don't see a module that adds the functionality you need (or if you're not sure), ask in our forums.
After that, spend some time reviewing the list of things to do post installation at Configuring Your Store.