You can find the crop image at the top of the application, it appears when you select an image. You can, of course, do this all in Photoshop etc but this feature means you don't have do the task in another application
Select an image and then click the 'crop image' button and set the region interactively with the bounding boxes. Set the PPI and click apply. You can move the region around by using the selection tool as well as re-sizing the region via the same tool. You can also use the top bar to change the region's position and size
Click the button and change the size / origin by editing the rectangle either interactively or via the values in the top bar. The area to be removed is in a lower opacity. The only setting that needs to be changed along the top bar is PPI setting in the top left and set that to 300 or 72 or 1 etc, it does have an effect on the end result. You can also constrain the height and width by clicking the link button between those settings in the top bar if you are using those controls or hold down the shift key is you are interactively applying the tool.
The best panel for this is to use the layers panel which can be found via the window menu and right side menu and duplicate command. Select the top duplicated layer and then click the button and then position and size it and press return. Go to the layers panel and disable that layer as I always find it tricky to use the tool when I have active layers. The key thing is that you must select the blue button to make the layer active and then you can apply the effect to that. If the layer is not properly selected then the region will be limited to the previous region. You can also combine this with effects, so select the active layer and apply an effect, this is probably more useful when you have disabled the layers above. The layer has had a Gaussian blur live effect added. Once you have finished with all the slicing and dicing of the images, set them all visible again (if they were hidden) and unless you moved everything the image should look much the same as before but now you can shift the layers or perhaps re-scale or rotate the individual images. You can also duplicate the layers as well as add effects to them such as shadows etc to create your final disjointed image. Unfortunately, you cannot record the effect as an action, the command is not (it seems) recorded when you create an action so any scaling or rotation etc is only applied to the source image.
You can also the above technique to create slices in the image. Instead of just randomly selecting parts of the image, you can use thin rectangles on different layers across the image and then remove the background. You can leave gaps between the rectangles to create a sliced look across the image
Click the button and set rectangle. You can then set the PPI to 300 etc and click apply. This may or may not be of any use for you depending on the end result. You can also set the PPI to a very low value which does creating an interesting mosaic effect. Note, the actual setting is done afterward as there is no preview until you press return, which generally doesn't matter but if you set the PPI to 1 say, the end result is only seen after you click return.