The Cold Survival skill is used passively it allows you to access surfaces and areas that might otherwise be inaccessible due to extreme temperatures.
Cold survival is used to access tiles that are very cold, such as ice or snow tiles. Someone without the proper training could easily freeze to death or not recognise the dangers such as avalanches and snow holes without this skill so that is why it is required.
See the image below for the list of terrains Cold survival is needed for.
Additional Information
As with all of the survival skills Cold Survival can be obtained from finding items that contain the Cold Survival bonus on them.
Cold Survival can also be acquired through mounting any of the following pets:
You can also consume certain food items and/or potions to acquire the Cold Survival skill, and infact there is a quest you can do in Knotwood Valley to get two potions that give you Cold survival skill for 24hrs).