Exercise- Moon

Step 1: select a photo.
Step 2: Use elliptical Marquee Tool, then press Shift and click on the area where I want to select (the moon)

Step 3: Go to Mask and click Select the pixel mask (1) to transparent the background. Click Make Edge to refine mask, you can check that the selection is transparent a not.

This is the result after the using the mask.

Step 4: Use patch tool to click and drag the area and to a smooth area where I want to replace it. While clone stamp Tool also have the same function. press ‘alt’ to select the part, then click and move to the part.