The port is what Trader68 uses to communicate with IB’s Trader Workstation software (TWS). If you are only trading one IB account, then in most cases you will just leave the port at the default setting. If you are trading multiple IB accounts with Trader68, then you’ll need to assign a unique port to each account.
To set the port within TWS select Configure -> API -> All API Settings… from the menu of the main window, then change the Socket Port. After you have made this change, make the same change to the Port # setting within the Account Details window (or the Account Setup Wizard).
You may also want to add your local computer as “trusted”, which will keep you from having to give TWS explicit permission every time you try to connect to the API through Trader68. To do this, click the Create button and enter 127.0.0.1 as the trusted IP address.