Without adjustment you camera will attempt to expose so that snow will come out grey or blue if it comprises much of your picture. To compensate for this you can over expose by 2/3 to 1 2/3 stops. The amount depends on composition and light intensity.
Use your histogram to determine how much over exposure you need. The peak on the right represents the white snow. Generally you want it close to, but not across the right side of the display to make snow look white, but retain some texture.
If your composition varies from scenes with mostly snow to mostly neutral toned subjects with just some snow you will have trouble using Av, Tv or P modes because the required compensation will keep changing. For this reason it is often best to shoot M mode in winter so you have more control.
One process to determine exposure in M mode is to first set exposure on the brightest part of the snow using spot or partial metering so that it is over exposed up to 1 2/3 to 2 stops. Then check exposure on neutral toned subjects to ensure it is reasonable. If not you will have to compromised between blowing out the detail in the snow and under exposing the other subjects. Often it is better to not blow out the detail in the snow and attempt to recover detail in the shadows in processing.
Shoot in raw format. It is easy to make exposure mistakes in snow and it is nice to be able to adjust exposure a bit when converting.