An infrared sauna and a steam room are indeed totally different things. As opposed to throwing water on rocks in a steam sauna, an infrared sauna doesn't work with heated rocks. They are fitted with infrared heaters which heat your body directly rather than by heating the air around you (like in a traditional sauna).
You can compare it with a sunny day when you feel the heat of the sun. When a cloud shifts in front of the sun, you feel less heat from the sun, but the temperature of the air around you remains the same.
Because infrared saunas heat your body directly, you can sweat more profusely while the operating temperature is lower. A lot of people feel that this is more comfortable and less claustrophobic.
Infrared saunas are often used in detoxification programs, because the deep sweat helps your body to get rid of toxins.
If you research infrared saunas on the internet, you will find a lot of promo-talk on websites of vendors, but this
infrared sauna website offers a lot of unbiased information and has no commercial interest in infrared saunas.