In the new Collections feature you will be able to collect Scrabble Coins and spend them in the Past Collections Book. The Past Collections Book contains various old collections (we are always looking at ways to improve this feature so we might add more past Tile collections in the future).
To win Tiles from past Collections you will need to use Scrabble Coins. These can be picked up in several ways, from duplicate tiles, as rewards in some game modes and also as offers in the shop.
All Tiles in the game will appear in your inventory, but they might not yet be added to the new Collections feature.