You can use primary fire to fire your weapon, and secondary fire to use spells. I use the spells more than the weapons, since ammunition is scare, and your Mana replenishes on its own. You acquire spells throughout your quest and you also can increase the power of the stones with the use of amplifier stones. Now, the puzzles can be easy to solve, but can also be rather difficult and require you to backtrack quite a bit at times. This can be frustrating sometimes, for I got stuck quite a few times, but after thinking for a while I figured out what I did wrong.
Controls are nice and solid, and are configurable.
They are based upon the standard FPS controls, and it is not hard to move around. There is a slight learning curve, but not much of one. It can be a tad hard to do some precise jumping, because I find it hard in FPS games to do it very precisely, but there is very little jumping needed to be done, so it does not make much of a difference. Overall, this game is a must get. This game is the scariest game I have ever played, and really lives up Clive Barker's legacy.