Actually it gives us both. It predicts the outcome of say double slit experiment but it also tells us the "mechanism". The "mechanism", if you can call it that

Actually it gives us both. It predicts the outcome of say double slit experiment but it also tells us the "mechanism". The "mechanism", if you can call it that, is the wave function, which is a complex valued function, norm squared of which is probability amplitude - roughly speaking the probability that the particle is located at a point in space. So what is really happening is the wave function is propagating though space and interfering with itself as if it were a "normal" wave (say water wave). So wave function propagates through the two slits in double slit experiment and the two resulting waves collide just like water waves would passing though the slits with the resulting troughs and crests of the wave function (remember this is complex valued function whose absolute value squared is the probability that particle is located at that location in space). So, in the quantum model, what is "waving" and spreading through space is in a way a probability of the particle being there. This explanation is very rough and contains a lot of inaccuracies (you really have to look at the math to know what is really going on) but it does give you some flavor of what is going on.