The difference between sleet and freezing rain is all about temperatures; more specifically, the air temperature above your head.
Sleet and freezing rain start as snow inside a storm cloud. This snow falls and runs into warmer air and melts into raindrops. Now here is where the differences start. The raindrops fall into a large layer of cold air that stretches to the ground. The raindrops freeze and turn into ice pellets. Those pellets also known as sleet are easy to ID because they bounce off the ground.
For freezing rain to form, the warm layer extends much closer to the Earth. Near ground level, the temperature is below freezing. This freezing layer is not thick enough to freeze the raindrop, so it falls to the ground as a liquid. The temperature of the ground/trees/power lines is below freezing, so the raindrops hit the surface and instantly freeze.
A thin layer of freezing rain can make roads nearly impossible.
Sleet can also cause icy roads but it needs to pile up for roads to get slick. With both of these precipitation types in the forecast, please drive carefully.