Learn the method of Ecshop source code, how to deal with

How to learn Ecshop source code
I want to learn the source of Ecshop in this period of time, where do I start to look? Just started to see a little dizzy, see for a long while did not see what effect

------Solution--------------------
I think you should be better off first.
APS, the first thing to do is to fill in the content of OOP
Functions and what needs to be mended, because some of the wording is slightly different from the ASP
It will be a lot easier to look at after the foundation is enriched.
------Solution--------------------
Ecshop, it is recommended to read the shopping cart first, bank payment, and then look at the structure of the table and so on

