The ENVI-Core is the central simulation software.
The first step to start a simulation is to select the project. (1)
Once the project is loaded (1), you can open the simulation settings file (.simx) (2)
Once this is loaded aswell, you can either check the simulation (1) or run it directly (2). It is normal for the ENVI-core to become unresponsive. The application runs fine in the background and you don't have to do anything.