One of the new mechanics introduced for The Legend of Zelda: Breath of the Wild is the concept of cold resistance when you enter certain areas of the map such as Mount Hylia. Without this ability, Link will quickly lose health, and eventually freeze to death if he stays in that area for an extended length of time.
In order to prevent this from happening, you will need to obtain a piece of clothing such as the Warm Doublet, or eat a meal that has cold resistance as one it’s additional perks. At the beginning of the game, it is highly recommended that you take part in the side quest to obtain the Warm Doublet, but there is a much simpler way to obtain the item without finding the recipe for the Old Man’s favourite meal.