The freezing point of water is 32 F degrees which is 0 degrees Celsius.
So when the temperature outside gets to 32 F degrees or below then water can freeze and ice can form.
So at 32 F degrees is the temperature at when ice can form.
If it's raining out and the temperature outside is 32 F degrees or below then you need to watch closely for ice to form on roads.
There can also be what is known as black ice which you cannot easily see and can cause you to slide off the road and even lose control of your vehicle or slide into other vehicles.
Be very careful when you are driving on ice or when ice can potentially form.