You can enter this code in one of two places. If your evaluation version has expired, the window which pops up when you run it has an "Enter Unlock Code" button. Simply click your mouse on this button and enter the code in. The other way to enter the unlock code if the program has not expired yet, is to click on the Help menu item, then click on Register.

It is easier to copy/paste the unlock code than it is to manually write it out. To copy/paste some text you simply need to SELECT the text you want to copy with your mouse (simply hold down the left mouse button and move the mouse over the text) then press the CTRL key combined with the C key. Alternatively there should be an EDIT menu on your program which has a COPY item in it.  Then to paste the copied text into Port Explorer, simply press the CTRL key combined with the V key after ensuring the cursor is flashing in the area you to copy it into.