If you have a double hung window in which each spring on each side of the sash is located, you need to take the window and tilt it to one side and put the little flat metal part into the side of the sash, Then begin to level the window and as doing this aline the other side of the sash with the other little metal part attached to the bottom of the other spring. Square the window up then flip up to close. Its a bit tricky to do, but once you have it figured out you will be able to do the new one real easy when it comes apart.
Positioning the "clip" part higher often reduces a little of the tension in the spring assembly. then proceed as woodbridge mentioned above.