The Crop tool can be set to constrain its values to a predefined or custom size. It can be left ‘Unconstrained’ however. There are various overlays, which include things like Rule of Thirds and Golden Ratio, all helping you to create the perfect crop.
The most important option to look at is the little checkbox ‘Delete Cropped Pixels’. If this is ticked, then you will destructively crop your image. Untick this and you can go back in at any time to change the cropping of your image using the pixels you had got rid of.
The Crop tool works slightly differently than it did before. Pulling the handles in to where you want your crop box and the image will reposition in the new crop area, making it really intuitive to make good crops.