First, if you do not know how to use the dynamic URLs, you should check Dynamic Url Structure. After choosing current mode as crop with c_crop you must define width and height of the image that you will produce with w and h parameters. Cropping is simply taking a smaller frame from original image, you can define the position of new frame by using x and y parameters. Entered x and y are coordinates of the beginning point which is top left corner of new frame. For example if you have a 300x300 photo, and your parameters are c_crop w_100 h_100 x_200 y_200. The image that you produce with these parameters will be a frame that begins at the 200, 200 point of original image and finishes at the point of 300, 300 which is the end pixel of original image.