Here's a simple sample Ladder Logic LD program. It starts when the PLC application starts and increments a counter variable every second.
Note this includes a Global Variable List (GVL) that has the CounterPLC variable (double integer DINT type). With it in the GVL, this will be available to other programs in the application.
For how to import, see this FAQ:
Here's a video it running within PAC IDE software:
Note a PAC320 hardware controller isn't necessary to run this. You can use an application with a CODESYS Control Win V3. Under Online > Simulation. Then you can after Build (F11), click Online > Login. This will create a virtual PLC and allow you to run PLC simulation (Play or F5). Here's a screen capture and project archive: