I've entered my creds and finally I successfully was connected.
Then I've create a test directory where I wrote my first create_table.sql file with vim.
In the next step I've started a new Putty-Connection to run the table script by entering 'slqp' on the command-line. Again I had to enter my creds for this SQLPlus session.
The first command which you should enter is the 'SET SERVEROUTPUT ON' command to get the corresponding output of the server after you have executed a query.
Then I've testet my create_table.sql file by typing 'start PATH_TO_FILE/create_table.sql'. If your sql-file successfully executed you can type 'exit' to exit the SQLPlus session.
To be continued ...