To activate SQL*Loader express mode, you can simply specify your username and a table name. SQL*Loader prompts you for a password, for example:
> sqlldr username TABLE=employees
Password:
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SQL*Loader: Release 12.1.0.1.0 - Production on Thu Jan 3 12:57:05 2013
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Express Mode Load, Table: EMPLOYEES
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If you activate SQL*Loader express mode by specifying only the TABLE parameter, then SQL*Loader uses default settings for a number of other parameters. You can override most of the default values by specifying additional parameters on the command line.
SQL*Loader express mode generates a log file that includes a SQL*Loader control file. The log file also contains SQL scripts for creating the external table and performing the load using a SQL INSERT AS SELECT statement. Neither the control file nor the SQL scripts are used by SQL*Loader express mode. They are made available to you in case you want to use them as a starting point to perform operations using regular SQL*Loader or standalone external tables; the control file is for use with SQL*Loader, whereas the SQL scripts are for use with standalone external tables operations.
SQL*Loader Control File Reference for more information about control files