The clone tool looks like a "rubber stamp" icon, screenshot inserted. If you hover the cursor over the tools their names pop up. To use the tool you have to click the area you are cloning "from" while holding the ALT key down, then move to where you are cloning to and press/drag around holding down the mouse button. You may need to reset the "from" part of what you cloning, depending how much you are editing (I almost always have to reset that. ) You may also need to use the zoom tool to go in tighter, depending how fine the detail in what you are editing.