Steam helps remove creases in clothes by relaxing the fibers and allowing them to return to their original shape. The heat from the steam opens up the fibres and causes them to become more pliable, making it easier to remove the wrinkles.
When the steam penetrates the fibre’s of the fabric, it adds moisture to the material, which helps to loosen the bonds between the fibres. This makes it easier to iron out the wrinkles and smooth the fabric. The heat from the iron then helps to set the fabric back in its original shape, helping to remove the creases.
In addition to the heat and moisture provided by the steam, the pressure from the iron also helps to remove creases by pressing the fibre back into their original shape. This is why a steam iron is often more effective at removing wrinkles than a traditional iron without steam.