program flow chart for opencart ?

Hello
Is there any program flow chart for opencart 1.5.6 ?

I read development guide about MVC-L and so on but i am
looking for more explanation.

Now when I change some code it can perhabs cause disastrous side effects.

thanks Peter

For example in file /catalog/model/checkout/order.php there is a class:
class ModelCheckoutOrder extends Model {......
with member function public function confirm( ..............

But which code calls confirm for after checkout customer email ?

I do a global text in file search but I cant find code like:
$model_checkout_order = new ModelCheckoutOrder ;

modelcheckoutorder refers to the file in model/checkout/order.php