Help and Support
The best place to start for help is by having look through the the in depth user guide, which contains an installation guide and detailed information on each function that is available from the flexi cart libraries.
If there is a feature available in flexi cart that you wish to implement on your site, then there is most likely a working demo example of how to implement the feature.
Have a browse through the demo and see if there is a example of what you are trying to achieve.
If you find an example of what you're after, then open up the downloadable demo files and have a look at the underlying code.
Still stuck? Contact me via the CodeIgniter flexi cart forum thread http://ellislab.com/forums/viewthread/212926