Make sure to obtain Propel Accelerator's port number beforehand by Clicking Here.

Setting Opera’s HTTP Proxy Address and Port Number

1. Click on the Opera File menu.
2. Select Preferences...
3. Click on the label for the Network catagory (the fourth from last choice)
4. Click the button labled Proxy Servers.
5. Make sure the Use Automatic Proxy Configuration checkbox at the bottom is unchecked.
6. Check the HTTP checkbox at the top.  Leave the other checkboxes unchanged (HTTPS, FTP, etc).
7. In the HTTP Proxy area, enter "localhost" (without quotation marks).
   
8. In the Port area, enter the Propel Accelerator port number.
9. Click OK.