You have Healing Brush Tool selected in your tools panel.
For Healing Brush to work, you need to sample the area you want to sample from first and you do it by holding Alt key on the keyboard and clicking once to take a sample. Then, you move the cursor and click to apply the sampling point.
Hi, first you need to select the part you want to sample. To do this, hold down the ALT key on your keyboard and then click the mouse to take the desired sample. Once this is done, apply the sample you have just taken to the desired point.