One of the great things about the Crop Tool is that you can easily crop your photos to common photo sizes like 4圆, 5x7 or 8x10 simply by entering the width and height values into the Options Bar before dragging out your cropping border, or by selecting a preset crop size from the Preset picker.
It's so common that Photoshop comes with a tool designed specifically for cropping photos, conveniently named the Crop Tool. Cropping images is by far one of the most common, every day uses for Photoshop.