It should be in Generators > Whatever Category you place the Dividers 2 *folder* in. (If you dragged the folder you get when you unzip the file, that will confuse FCPX -- it will think sc_dividers2 is a *Theme* and organize the file differently than suggested.) If you created a new category folder, the name of that folder shows up in the list of generator "types" in FCPX. You can also try finding it under "All".
The image above is the generator overlaying the storyline (which is a video clip AND a title that I'm developing applied - the generator is placed over both). Two of the regions were left with the color background regions "turned on" (opacities set to 100%) but each of the 4 regions has a separate background available. It is possible to animate these color backgrounds' fades, turning them on or off at will, by keyframing. Other than that, this generator is just 3 lines -- the horizontal, and two verticals. All of the lines can begin or end off-canvas, so if you need a 2-way split, drag the horizontal line off the bottom or top of the screen. If you need vertical 2-way, drag the vertical bars off either side of the canvas.
If you are applying video to fill the splits, those clips would be place *under* the generator. Use the Transform and Cropping controls to line up the edges under the divider lines. You can use the solid color regions as a fade or reveal from color to media. If you don't need to line up everything exactly, you can make use of the color backgrounds and transform the media smaller to fit over the color (place clips over generator in that case). There are onscreen controls in the canvas to make working with these transfroms easy (under the left corner of the canvas are a set of icons for Transform, Crop, Distort [or in FCPX 10.0.6, it is now one of those icons and a drop down menu to choose the others from.])
If you decide to experiment with rotated dividers? Apply a Keying > Mask to the clips and edit the mask to fit behind the divider lines - OR - use Tranform > Rotation to fit the clips with the same rotation as the dividers.
It's all very quick work once you get used to it.
HTH