This is a very low quality image. Although you can use "Select/Color Range" and click on the white part to select the whites, it will end up selecting what appears to be a transparent background which it is not. You are better off recreating the image.
Create a document that is large enough for your needs
Add a new blank layer by clicking on the new layer icon that looks like a square within a square
Pick the marquee tool and change the marquee to an ellipse
Hold the shift key to constrain it to a circle, click and drag while the shift key is pressed from top left to bottom right to draw a circle
Pick up the fill tool and white foreground color and click inside the circle to fill it with white
Your selection is still active, pick up the marquee tool again, hold the shift key and drag the selection from inside of it to the right until it marks the crescent area on the left
Press the delete key
You will end up with the white crescent on transparent background. It will take you probably 3-4 minutes at most to create it while reading the instructions. That will be a crescent of the right size and shape for your needs.
Assuming that you are working directly from the image you've added, and have not moved anything.
Use your arrow tool and click on the orange circle. The outline of the shape should be visible. If not, be sure to allow selection of your active layers on the top left of your dashboard.
Use your path selection tool and select the entire circle. The anchors should turn to black squares.
Copy (Cmnd-C) the shape. From here you turn the orange shape layer off.
Select the white circle with your arrow tool.
Use your path selection tool and select the entire white circle. The anchors should turn to black squares.
Paste ( Cmnd-V ) the shape originally copied path over the white circles path.
After you've pasted the path on top of the white path, without selecting any other tools so that the paths are still active, use the shape icons that are on the right of the W: and H: tool on the top tool bar. User the subtract front shape.