You don't need an actual PLC hardware when you want to use PLC simulator to test your program. However, you want to make sure that you have configured the hardware (in the STEP7 software) properly and have added the required modules such CPU and input and output modules.
Once you have the hardware (in the STEP7) configured, you need to compile it, save it and then download it to the simulator.
Then in the simulator, add some inputs and outputs and start testing the logic after you have downloaded the logic to the simulator.
I recommend that you watch this video in the library for more details: https://realpars.vhx.tv/videos/54-plc-simulator
Let me know if you have more questions.