So to add to sophie's answer.. Stretch denim usually has 1-3% elastane or spandex in the cotton. It's still jeans. They will look exactly the same, you just might notice they stretch a little easier at the seams, knees, waist, etc. They will look no different than 100% cotton jeans to the naked eye.
Stretch denim just means there is some Lycra woven in with the cotton. They will be a little more stretchy and comfortable but will still be whatever cut they are said to be. For example bootcut jeans will still be bootcut.
