HOW-TO: use mod_rewrite to get rid of "?" in the url

Hi
i do all steps in this url When I click some button or follow some link, I'm left with a blank page. What do I do?
and the error appear

ojs2 has produced an error
Message: WARNING: session_start(): Cannot send session cache limiter - headers already sent (output started at /home/onlin170/public_html/ojs/lib/pkp/includes/functions.inc.php:25)
In file: /home/onlin170/public_html/ojs/lib/pkp/classes/session/SessionManager.inc.php
At line: 60
Stacktrace:
File: (unknown) line (unknown)
Function: PKPApplication->errorHandler(2, “session_start(): Cannot send session cache limiter - headers already sent (output started at /home/onlin170/public_html/ojs/lib/pkp/includes/functions.inc.php:25)”, “/home/onlin170/public_html/ojs/lib/pkp/classes/session/SessionManager.inc.php”, 60, Array(3))
File: /home/onlin170/public_html/ojs/lib/pkp/classes/session/SessionManager.inc.php line 60
Function: session_start()
File: /home/onlin170/public_html/ojs/lib/pkp/classes/session/SessionManager.inc.php line 130
Function: SessionManager->SessionManager(Object(SessionDAO), Object(Request))
File: /home/onlin170/public_html/ojs/classes/security/Validation.inc.php line 281
Function: SessionManager->getManager()
File: /home/onlin170/public_html/ojs/lib/pkp/classes/core/PKPPageRouter.inc.php line 66
Function: Validation->isLoggedIn()
File: /home/onlin170/public_html/ojs/lib/pkp/classes/core/Dispatcher.inc.php line 117
Function: PKPPageRouter->isCacheable(Object(Request))
File: /home/onlin170/public_html/ojs/lib/pkp/classes/core/PKPApplication.inc.php line 178
Function: Dispatcher->dispatch(Object(Request))
File: /home/onlin170/public_html/ojs/index.php line 65
Function: PKPApplication->execute()

and

ojs2 has produced an error
Message: WARNING: Cannot modify header information - headers already sent by (output started at /home/onlin170/public_html/ojs/lib/pkp/includes/functions.inc.php:25)
In file: /home/onlin170/public_html/ojs/lib/pkp/classes/core/Dispatcher.inc.php
At line: 247
Stacktrace:
File: (unknown) line (unknown)
Function: PKPApplication->errorHandler(2, “Cannot modify header information - headers already sent by (output started at /home/onlin170/public_html/ojs/lib/pkp/includes/functions.inc.php:25)”, “/home/onlin170/public_html/ojs/lib/pkp/classes/core/Dispatcher.inc.php”, 247, Array(0))
File: /home/onlin170/public_html/ojs/lib/pkp/classes/core/Dispatcher.inc.php line 247
Function: header(“HTTP/1.0 404 Not Found”)
File: /home/onlin170/public_html/ojs/lib/pkp/classes/core/PKPPageRouter.inc.php line 184
Function: Dispatcher->handle404()
File: /home/onlin170/public_html/ojs/lib/pkp/classes/core/Dispatcher.inc.php line 134
Function: PKPPageRouter->route(Object(Request))
File: /home/onlin170/public_html/ojs/lib/pkp/classes/core/PKPApplication.inc.php line 178
Function: Dispatcher->dispatch(Object(Request))
File: /home/onlin170/public_html/ojs/index.php line 65
Function: PKPApplication->execute()

can you help me please