GDB connects to all simulator targets using the same basic command, although each simulator may require additional options. These are listed in the document describing the target, and should be used when connecting.
Connect to the target by issuing the following command in GDB console mode:
(gdb) target sim [target specific options]
In Insight, connect by opening the File->Target Settings window and enter:
Target: Simulator Options: [target specific options]
Set other options according to preference, close the window and select Run->Connect to target.