I simmer always at low heat?

For a risotto it should be creamy not wet when you spoon it on to a plate it should slowly spread I agree that the liquid should be hot at a low simmer almost to the point were its just hot not boiling

I think the tag here was "risoto" (sic). A risotto should be cooked "al onda" or on the wave as they say in Venice. Which means that you add simmering (not boiling) stock, ladle by ladle until it's finished; at least 20 minutes, but it should be wet and moving around when served.

Good answers if you want the liquid to evaporate and thicken you could also simmer uncovered

For a simmer, the usual procedure is to start on high and bring the ingredients up to a boil or near boil, then turn the heat down low and let it barely bubble. Often you will set a lid on the pot, slightly askew, to prevent to much of the liquid from evaoprating.