
The Gradient Tool is located in the same spot as the paint bucket tool. If you hold down the paint bucket tool, the gradient tool will appear. Select this. By default, the gradient will be your foreground and background colors. You can edit your gradient by clicking in the gradient editor.
This is the Gradient Editor. Create a purple sky that fades to blue and white. First select a color stop (1). Then select the color swatch (2) to bring up the color picker (3). For this, choose white. For the light blue, click on the area below the bar (4) to create another color stop and then use the color picker to select a light blue. Repeat the same for light purple.
Now make sure that you pick the linear gradient so the gradient goes from one end to the other.
First make sure that you are on the "Sky" layer you created earlier. Next, drag from point A to point B.
And now we have sky.
Go to File > Save as… and save your work as a .psd.