Thanks for contacting us! In order to use the Clone tool, you first need to click on the source (what you want to copy – in this case a cat). Then you need to paint on the copy wherever you want it to appear (by holding down the mouse button and dragging).
To add another copy, you need to click the Source Selection button, click the source again (the original cat), and again paint on the copy wherever you want it.
Let us know if anything’s unclear or if you have any further questions!