Hi,
If the question is how the entries are created (inserted) in Customer Ledger Entry
Ans: When you post a Sales Order then Code Unit 81 is used, which in turn calls codeunit 80 and then later on Codeunit 12 creates those entries in Customer Ledger Entry (CLE).
I suggest you to either use the Code Coverage (Tools >> Debugger >> Code Coverage) or Debugger for learning the process of posting a sales order.
or Did you wnat to ask as in previous post, how the Balance is updated from Customer Ledger entry?
Hope this helps