What exactly do quotation marks around the table name do?

Answer

Under the covers, Oracle is always doing case-sensitive identifier matching. But it always casts identifiers that are not double-quoted to upper case before doing the matching. If you put double-quotes around an identifier, Oracle skips the casting to upper case.

So if you do something like

CREATE TABLE my_table(
  col1 number,
  col2 number
)

you can

SELECT * FROM my_table
SELECT * FROM MY_TABLE
SELECT * FROM My_Table
SELECT * FROM "MY_TABLE"

but something like

SELECT * FROM "my_table"

will fail.

On the other hand, if you do something like

CREATE TABLE "my_other_table"(
  col1 number,
  col2 number
)

you cannot do

SELECT * FROM my_other_table
SELECT * FROM MY_OTHER_TABLE
SELECT * FROM My_Other_Table
SELECT * FROM "MY_OTHER_TABLE"

but this

SELECT * FROM "my_other_table"

will work