Assuming you are referring to a button in a newer car that says snowflake on it:
This button is typically found on cars equipped with all-wheel drive (AWD). When the snowflake button is pressed, it tells the car's computer to send more power to the rear wheels than usual. This helps the driver maintain control of the car when driving in slippery conditions, like on ice or in deep snow.
How much power is sent to the rear wheels varies depending on the make and model of the car. In some cases, pressing the snowflake button will also cause the front wheels to turn slightly inward, which can help prevent them from slipping sideways.