Here are some explanation on the terminology:
Cut: to select and remove a part of the drawings.
Copy: to select and duplicate a part of the drawings
Paste: after you choose to "Cut" or "Copy" an image, you can stamp (paste) this image again
multiple times on different places in the same frame.
Rub: after you choose to "Cut" or "Copy" an image, you can rub this image on the surface of the canvas. The effect is like pressing the image on a piece of paper, and only the parts that are being pressed will be shown on the paper.
Please tap on the rope on toolbar on the right side, select the part of the drawing that you wish to copy or cut down. Tap the Camera icon to copy and image, and the Scissors to cut the image.
Copy the Image
Tap the Camera icon to copy the drawing. After that move the copy to the place where you want to paste the drawing.
You can choose to stamp (paste) the image of rub in the image.
If you choose to rub the image, here is how to do it, and result.
Simply draw on the image, only the part of image pressed by your finger will be rub on the canvas.
After you are done, tap on "X" to exit the the selection mode. You can now do other editing.
After the image is cut off, you can choose to paste it or rub it on other part of the canvas.
Stay in the selection mode, you can move to other page to paste or rub the image.