Which process read data from the data files in Oracle

The execution of a SQL statement goes through four stages:
PARSE
BIND
EXECUTE
FETCH

Parse phase Server process works out what the statement actually means, and how best to execute it. Parsing involves interaction with the shared pool of the instance.

Bind Phase any variables used in SQL Statement are convert to its actual literal values.

Execute & Fetch phase During the execution of a statement, data in the database buffer cache will be read or updated, and changes written to the redo log buffer; but if the relevant blocks are not in the database buffer cache, your server process will fetch data into the buffer cache from the data files.