LiveCart has been developed keeping developers needs in mind. Most of currently available shopping cart programs are a pain to modify, because they lack clear structure, contain a lot of ad-hoc spaghetti code all over the place, do no provide clear interfaces for hooking in your own functionality, no APIs, not to even mention a system documentation or at least well commented code.
We have attempted to solve this problem for once by creating a truly developer friendly application, with well structured code, which follows strict conventions, providing means to extend or interact with the system without a need to change the underlying code as well as providing as much documentation as possible to make it easier to get around in LiveCart code.
If you're looking to do mode complex customizations, you should introduce yourself with LiveCart architecture and basic principles first.
LiveCart provides standard interfaces for plugging in new classes for extending application logic, business object (model) login as well as adding support for additional payment processors and real-time shipping cost calculation.
Unless you need your store to support some special features or integrate with other systems, you won't need to touch any code or, in fact, write any code.
There are many other ways to customize your LiveCart installation. You'll find more information on this in Customization section of this manual.