By clicking on Simulate in the schematic the software run a momentum simulation for imported components associated to a circuit simulation, don't worry about the simulation process.
Just draw the layout in momentum with number of port correponding to number of connection you will need to put your components.
Via hole? via hole is used to connect something to the ground if you are in microstrip line, i don't understand , tell me more
You have to define via hole if needed, all your design will be imported in schematic