Explore dungeons to earn valuable rewards. Treasure chests and materials reset weekly. You can collect Delve Currency from dungeon chests and spend it in the Delve Store.
Delve Currency can be found in any discoverable dungeon. To locate these dungeons, open the map and look for the purple gate icon. You can check the screenshot below for an example.
You can also filter the map to show only dungeons. Open the map, go to Map Settings, and uncheck every option except Dungeons. This will make dungeon locations much easier to spot. Once you're done, you can re-enable the other map icons at any time.