You can use the "Collections" menu to check your progress on the Dream Garden island!
Different sections will show your progress in certain parts of the Dream Garden Island. If you don’t know what to do, or you don’t know why you need a certain object, you can open the "Collections" menu to check your progress.
New objects in the "Collections" menu will be unlocked right after you create those objects by merging previously unlocked objects. You will receive a small reward for unlocking a new object.