Ironing means getting the creases out of clothes after they have been washed and dried. Ironing is done with a tool called an "iron". It is called an iron because the bottom part is traditionally made of iron, a type of metal. The iron is heated before it is used. This used to be done by putting the iron on a fire. Nowadays electricity is used to warm the iron. The water inside becomes steam.
Ironing clothes is usually easiest when the clothes are still very slightly damp, but it depends on the material of the clothes. There is normally a label on the clothes which shows whether it can be ironed, and at what temperature. The clothes to be ironed are put on an ironing board and the iron is pushed carefully along the clothes to get all the wrinkles out. Ironing is usually done with an ironing board.