What does the D3 on on the gear shift of my car mean?

Apparently tomorrow morning my area is expecting freezing rain as well as snow. I drive an SUV. There is a designated snow on on my car that adds more traction but I was wondering what the D3 means. I think it has to do with something called overdrive? Does the D3 on help with snow/ice conditions. Also would switching my gear shift to 2 or L help at all? I just turned 18 and am a new driver with little experience in snow. Thanks!