To get to the Source Code Lookup Tab (Which is the third of 4 tabs you will see in order to set up your FusionDebug connection), you have 2 main options:
Navigate to Run > Debug Configurations in Eclipse. See Figure 29 below.
Alternatively, you can go to the green debug icon, in your Eclipse toolbar and click the small arrow on its right-hand side. This brings up a small menu and you can select the Debug Configurations item from there.
Once the debug dialog is visible you can bring up the Source Code Lookup tab by opening the FusionDebug item and clicking on an existing debug profile, or by right-clicking on the FusionDebug item and selecting New from the menu.