Every day, you can pick one item from each category and press "Accept" button.
Every day you get notification same as for Daily Challenges.
Once you have accepted the items you have to spend enough andermant on anything and get the items from each category.
When you spent enough andermant (see the vertical progress bar) you get notification and you can accept the item.
There are three categories:
If you select items worth: 500 from copper, 5000 from silver and 25000 from the gold category that is total of 30500 andermant. You have to spend that amount of andermant (or more if you like) in order to get all the rewards.
You can see a copper and silver bar-like objects on the main vertical bar. Those are the limits for each category. You can place your pointer over them to see what is the limit for each category. The top is the limit for the gold category.
So you will have to spend 500 to get the first reward, then another 5000 to get the second reward and finally another 25000 andermant for the last gold category.
You get the items in that order. You can't spend 25000 andermant just to receive the last item from the gold category. You must receive the copper reward first then the silver reward and finally the gold category reward.