Both SQL and /SQL*plus allow manipulation of values in the database.
/SQL* Plus recognizes SQL satement and sends them to the server; SQL is the Oracle proprietary interface for executing SQL statements.
/SQL* Plus language for communicating with the Oracle server to access data; SQL recognizes SQL statements and sends them to the server.
/SQL manipulates data and table definition in the database; /SQL* Plus does not allow manipulation of values in the database.