Crop Tool

You may notice that, after you rotated your image in order to straighten it, we now have some white canvas areas around the outside of the photo. We need to fix this problem by removing those areas; for this we use Photoshop's Crop Tool. You can find the Crop Tool from the Tools palette, or simply press the letter C on your keyboard to select it with the shortcut:

With the Crop Tool chosen click near the top left corner of your image and drag down towards the bottom right to create a border around the part of the image you want to keep. Fine-tune your selection by dragging any of corner handles or by dragging the top, bottom, left or right sides of the selection:

Use the Crop Tool to drag out a selection around the part of the image you want to keep. Once you've dragged out your cropping border, press Enter (Win) / Return (Mac) to have Photoshop crop the image.

Have a look at this Video from You Tube on how to use the Crop Tool