Check the material of your shirt by looking at the tags of the shirt.
Find the appropriate heat setting for your shirtís material. Usually, the settings are clearly labeled on the iron, but you can check the ironís manual if needed.
Dial the ironís heat setting accordingly.
Set the iron to the steam setting.
Pour the appropriate amount of water into the iron. A collapsable paper cup works nicely for those small water inlets. Ironing a typical dress shirt usually does not require more water than the minimum amount required for the steam iron. Note: leaving a lot of water in the iron for long periods of time may lead to mold growth in the iron.
Plug in the iron.
Turn on the iron and allow it to warm up. You can test if the iron is ready by simply ironing an open area of the ironing board (off to the side); and if steam steadily flows from underneath the iron, the iron is ready for ironing. If the iron is not ready some water drops may leak from the holes in the ironing plate.