As chilli says above. You need 200 points for a free day in the winter. (Can’t remember how many points you need for a free day in the summer)
You earn 15 point per day in the winter. (It’s less in the summer, again I can’t remember how much)
If you’re staying with a chalet company, don’t let them buy your pass on you behalf. The passes they get are usually not applicable for the bonus points. If you already have an electronic pass you used in the summer, take it with you and give it to the ticket office when you buy your ski pass. They will add the extra points to it.
Also they don’t just give you the free days automatically. You have to ask for them. When I have redeemed my points in the past, IIRC you can only do one free day at a time. So if you have say 400 points and intend to take 2 winter days, you have to go back to the ticket office each morning and ask for a free day.
It is also possible to get a discount in the summer, if you have had a winter season pass in the same year. Although you’ll have had to fork out several hundred Euros for one of these and probably stayed for an entire winter season.
Hope this helps.