@CK97 There were three different components to it:

Challenges, where you could challenge other people in challenge missions, wherein you'd submit your score or time (depending on the challenge) and others would compete against it (complete with the ghosts of the challengers doing what they did when they did the challenge).

You could take and submit a photo for a rating. When you're out and about in the game's world you might stumble across photos from others (marked by a ghost standing or floating), see it, and give it basically a like or dislike.

And finally the treasure hunts - arguably the most interesting. About every 12 hours, you'd get 4 (or 8 if you've progressed to a certain point in the game) treasure chest hints. Activate one, and your warped to a random part of the world and you're tasked with trying to find the treasure chest, with only a photo of it from another player to go by. This mode was a lot of fun, as finding those chest can be rather tricky as they could be anywhere (including walls and ceilings) on a floating island. And once you've found it, you can take a pic of it yourself (while trying to get any landmarks to help track it in frame too) and send it off to be used by another player.

Almost all of the above rewarded you with Dusty Tokens in some way. Winning challenges netted you a good amount (with a tiny bit for tying and even less for losing). Rating a photo gives you a tiny amount, but getting a nice (liked) rating gives you a lot more. Submitting a treasure hint gives you a tiny amount, but having someone successfully use your hint gives you a lot. Actually opening the chest doesn't give you tokens, but instead a reward of some kind (most of which were unique to chests).

...I suppose all of this should have been written in past tense, now. Alas...