The Data Control Language is for data security and has four commands: GRANT, REVOKE, COMMIT, and ROLLBACK.The first line of security is the users for whom you GRANT or REVOKE access and update privileges to your data. Some people should never have access to your data while others should have only restricted access. Some people can only see certain data while others have the right to update that data. Only someone like your Database Administrator (DBA) and the owner of the company should have access to all the data.

If you create a schema, you are designated as the owner of that schema. As the owner of the schema, you can grant access privileges to other users. All privileges are withheld until they are explicitly granted by you. A users must go through an authorization process to prove their identity before they can perform the functions you have authorized. You can revoke any privileges you have previously granted.
If you GRANT use of the SELECT command, a user can see a database object such as a table or view.

If you GRANT use of the INSERT command, a user can add table rows.

If you GRANT use of the UPDATE command, a user can modify table rows.

If you GRANT use of the DELETE command, a user can delete table rows.

If you GRANT use of the REFERENCES command, a user can see data where SELECT has been granted to a table and that table references another table.

If you GRANT use of the USAGE command, a user can allow or disallow use of domains, user-defined character sets, collating sequences, and translations.

If you GRANT the ALL command, you are granting all privileges to this user.
You can REVOKE any of these privileges from users.

COMMIT and ROLLBACK make changes permanent or reverse the changes.