The command slic -n will start the simulator in interactive mode, where Geant4 commands can be typed into the terminal. When you use this command, you should see the Geant4 prompt.
PreInit>
The "PreInit" means that the geometry and physics have not been loaded, so Geant4 is in a pre-initialization state.
If you specify the geometry file with the interactive mode, then the simulator will be intialized for you.
slic -g mygeom.lcdd -n
This command should result in the idle state.
Idle>
From the idle state, it is possible to start the simulation by using the /run/beamOn command, or execute other commands that are valid for the idle state.