In your tutorials, we have a case of only one ledger in the whole GL, and this single ledger has been defined as a Primary ledger.

I am implementing Oracle General Ledger module. I have a combination of companies, which differ in their 4Cs in a manner that I have to create three ledgers (assumption agreed!).

Do I have to define the remaining two ledgers as respectively Secondary and Tertiary?
Or, do I have to define the other two remaining ledgers both also as Primary ledgers?

My instant is telling me that all the three ledgers should be defined as Primary ledgers; but not sure if I am right or wrong.

Please, explain with a bit of examples.

Thank you so much.

You will define the other two ledgers as a normal (Primary) ledger through Accounting Setups -> Create Ledger screen.
Reporting Ledgers and Secondary Ledgers are two different things.
Common Attributes:
Both Reporting Ledgers and Secondary Ledgers are attached to a Primary Ledger.
Journals are automatically mirrored in both kind of ledgers
Differences:
Reporting Ledgers could only differ in Currency with the Primary Ledger. While, secondary Ledgers could differ in any of the Cs from the Primary Ledger.
Summary:
If you need a representation of your ledger in another currency then you will report a reporting ledger.
If you need another representation of your ledger where other Cs differ as well besides the currency then you will create a secondary ledger.

Hasan, thank you so much. You have explained the concepts so very well. I am grateful to you. No more question on this!