RE: What do all of these do?
Maltodextrin and dextrose are both forms of carbohydrate, and they are both termed 'simple', which relates to their structure. But to athletes it basically means they are rapidly absorbed into the blood and cause a rapid insulin spike. As with all macronutrients (carbs, protein, fats) they do not cause weight gain on their own. Weight gain occurs when the calories taken into your body are greater than the calories you use, so you have a surplus with which you can grow. If you increase your intake of dextrose and maltodextrin but your total calories taken in are still below what you use, you will not gain weight. If you are eating enough to grow, then maltodextrin etc can be helpful.
These forms of carbs can be taken in your Post Workout (PWO) shake to help replenish muscle glycogen and cause an insulin spike to shuttle other nutrients into the muscle. So in that sense they are useful in aiding growth.
Whey is a form of protein used to supplement dietary protein. It is also rapidly absorbed so once again it is useful in PWO shakes.
Creatine is a natural substance found in cells, but can be supplemented. Do a search on creatine to find out more. They are two very different things and cannot be compared.