The simulator is just a spice simulator, it doesn't do any kind of characterization of the PCB to determine parasitics if that's what you're after. Well, it has some SI and PDN analysis tools, but those are only analysis and not simulation AFAIK. So if you want to simulate with parasitics you'll need to incorporate those into the schematic the old fashioned way.
I messed around with the simulator a bit, but honestly it was too much trouble to import the required models, also some of the parts I was interested in at the time didn't have models in a format Altium could use. I remember the process being kinda clunky and poorly documented, so unless you're going to be doing a lot of simulation it's probably faster just to use ltspice or whatever instead, and deal with having to re-enter the schematic.