Someone, please tell me what meaning is to be understood by alphabetic letters' and numbers' following a Family Surname?

Are you talking about something like:

Albert Hatchett Sr.
Albert Hatchett Jr.
Albert Hatchett III
Albet Hatchett 3rd

and such?

They are post nominal suffixes to help distinguish one person from another.

Thanks for responding . No, I'm referring to something like this after a surname......Smith...Bb-c6??

Do you know what it might mean if both parents and child have numbers like these following their names'?

If you are seeing that in a Family Tree it is probably some numbering system the tree owner is using.

If you are seeing it on a document it would depend on what type of document and the jurisdiction of the issuing agency.

Thank you for your explanations and your help!