Design Page Curves – Adobe Photoshop
Draw a box shape using pen tool. Clicking p will select pen tool in photoshop.
Now you can add editing points to it because its not a regular shape but its editable.
Add points by Add anchor point tool beneath to pen tool in its sub menu, at the corner where you want to curve to appear (e.g. slightly near from top right corner and slightly near right side under top right corner).
Select top right corner by Direct selection tool and drag it inwards.
Add gradients at that corner. Two gradients I suggest. One darker one at top and lighter one, beneath dark gradient by Gradient tool. You are done.
Download psd example file and see how I have made it.
Draw a box shape using pen tool or by rectangle tool.
At right corner as in my case place a white little rectangle so that it covers a part of right corner exactly. I have used polygonal lasso tool to select further triangle from that small box. Now I had white background. I placed white box at corner of blue box. I created inward selection of triangle from that box and gave it dark blue color. That curved triangle piece which you can see in image below was that selected triangle. After giving it some shadows and applying some layer modes and gradients you can get exactly the same result as shown below.
Download psd of this example to see how I have done it.