When I happened to come across my first builder event, I had more difficulties than with usual events to understand what I was supposed to do and where exactly to do what.
After several rounds that’s very easy now, and yes, there is some information about it in the game itself, and from Pixel here in the forum also.
https://forum.pixelfederation.com/diggysadventure/d/192837-winter-builder-4-migloo-under-construction
Edit: I just found another, much more detailed info by pixel here:
https://forum.pixelfederation.com/diggysadventure/d/192859-builder-event-all-you-need-to-know
End edit.
Still, maybe my experience may help some, so here it is:
(I play mobile on the app)
Like other events you can enter this one via the maps symbol down at the bottom of your game (green), then you tap on the map of Winter Builder 4 (red). ⬇️

The map opens and shows you the igloo location (red) , 3 story locations (green) and 3 repeatable locations (yellow). ⬇️

At the start, this will look different to you, as several locations will still be locked.
You start your story line with „Arctic Archipelago“, and like with other events or the main story line, when you have finished the quest in there, the next location „Icy Peaks“ opens. Also the first repeatable mine „Arctic beach“ opens.
In this way, when you finish Icy Peaks, the next story location „Ancient Frozen Caves“ and the next repeatable „Chilly Hills“ will open. After finishing the last quest, the last repeatable „Permafrost Caves“ will open.
In the story mines and in the repeatable mines you can collect „Divine snow“.
I just call it ice, you will have to live with that 😉
Usually you can use collected stuff for cooking or smelting or buying things.
With the builder items that is different.
The ice that you collect is used together with the ice that all players of your region collect for one big 8 floored region-igloo.
To do that, you give away the ice (for the igloo to be built) and get special coins for it instead.
With these coins you can buy camp equipment or jewels or green rings or food.
👉 Where to go next?
For this exchange process you go to your camp (tent down at the bottom of your game)
On the right side there is an igloo icon with a timer.
If you have collected ice, it should show an exclamation mark.
You can tap on this igloo icon any time for information, to exchange ice into coins, to collect keys for the igloo floors, to see the building progress and to see the ranking of your region.

Tap on the igloo icon, it opens with the overview: ⬇️

You see that my region has achieved to build 17,3% of the igloo.
As the building is divided into 8 floors, there will one floor open for every 12,5 %.
So the first floor is open to me already. You can see that in the igloo picture.
On the left you can see that I have collected all 8 keys already.
Still, as long as no more than the first floor is built yet, there are no floors 2 - 8 yet, and so I can enter floor 1, but have to wait for the upper floors with the rest of my keys at the ready.
At the start, you don’t have a key. You get them as a reward for exchanging enough ice for coins.
You see the Exchange button down in the middle. It’s grey on my screenshot, as I have exchanged all ice that I had for now and so I have no more at the moment.
If you collected ice in the story mines and in the repeatable mines, this exchange button will be blue.
Tap it to exchange 10 ice for 10 coins. Do it until you have exchanged all ice into coins.
There is no use in saving or collecting the ice. It‘s only purpose is to be building material for the igloo, so don’t keep it. The more ice players give, the faster the igloo is built. Also the more coins you have. That’s what the repeatable mines are for. And for most players, the equipment that you can buy with them is pretty strong. (Endgamers usually miss out on this fun, unfortunately.)
You will see on the left side, that with exchanging ice for coins the key symbol becomes available for you. When the circle is full gold, tap on it to get the key.
Edit: With each key, you get an achievement reward in the museum/trophy room.
👉 Where to go next?
When your region has built a floor and when you have a key for that floor, you can tap on the drawing of the igloo. („Tap to visit the monument“). You could also go to the maps again and to the „Giant Igloo in Progress“ location (see second picture above ⬆️⬆️).
There you can enter all floors that your region has built already, if you also have the keys.
Nice rewards are waiting for you there. They get better, the higher you get. On the last floor there is the Platinum ticket waiting for you. You get the best Builder equipment with it.
You can buy all equipment as well as jewels or green rings with the event coins (and with the Platinum Ticket) in the shop, choose the „New“ tab.
Additional information:
As said before, the igloo icon on the right side of your camp contains lots of information.
You saw the „Overview“ screenshot above already. On the right side of that, you can tap on the globe and see the „Battle of regions“: ⬇️

You can see that my region managed 17,4 % now. On the left you are shown a medal, if you belong to the top contributers of your region. Take it as a virtual honor or forget about it, as you wish.
You don’t get anything for it. Same goes for the ranking of the regions.
Next tab on the top is INFO ⬇️

There are six little pages of info and it’s way shorter than my sermon here 😄
Last tab on the right is a checklist ✅ ⬇️

This is as far as you can get on your own.
Often players ask for help: „I have all keys but the floors are still locked!“
You should know by now why that is. If not, here is additional help with that
https://forum.pixelfederation.com/diggysadventure/d/192855-unlock-rooms-in-the-igloo