During a winter season precipitation can fall in many forms.
Depending on location, precipitation can be from fog to hoarfrost and from snow to hail.
For the greater part of the continental United States, it is mostly in the form of snow sleet, freezing rain, and rain.
Factors that produce these four these types of precipitation
The first necessary part is that there is snow falling in the upper atmosphere.
Without any interference it will fall to the ground as snow.
The interference is a section of warm air below the upper atmosphere snow event. The thickness, level, and position, of warm air will produce the other three forms of precipitation.
If the warm air is above the surface and far enough off the surface it will produce sleet, snow that has melted part way and continued to the surface without much melting. Sleet can be from slushy snow to hail like snow pellets.
Should the snow melt enough to become droplets high enough and fall through enough freezing area to become ice again then you will have sleet.
Freezing rain starts as snow, changes to rain, stays rain till it meets the ground or objects, and if cold enough conditions are present refreezes on contact. This is still considered freezing rain.
Then there is snow that falls through enough warm air to be all rain and not freeze on contact. This is considered just rain.
To sum it all up
1) Rain
If snow falls through enough warmer air and the surface temperatures are also above freezing, you have rain.
2) Freezing Rain
Snow may fall through a large area of above freezing temperatures above and become rain. But when reaching the surface area, if there are sufficient freezing conditions, the rain will freeze on contact and be freezing rain.
3) Sleet
Like the conditions that change snow to rain, if the areas above the surface are sufficiently freezing in temperature then, the rain will refreeze and land as sleet.
4) Snow
Snow is snow if not affected by temperature on the way down it will be snow upon landing on the ground.
Depending on the density and the thickness of the layer of warmer air, if it should it be present, can make snow fall as freezing rain, sleet, or rain.