Lookout supports a list of PLCs. Different driver of PLC supports different hardware connection, serial or ethernet.
There are many exampls that show you how to build such application, including PLC communication, HMI, controlled process, data logging, alarm, etc.
Finish the attached Evaluation Guide to get a general idea of this product. The developer's manual installed with this software contains more detailed things.
If you have PLC, it's easy to make the connection. If not, you can use modbus slave object in Lookout to act as modbus slave hardware, and then use Modbus object in Lookout to communicate with the slave.
Ryan Shi
National Instruments