What are Orbs?
Orbs are used to complete quests which grant you the Blessing of the Seeker. You can obtain them through quests, and also get them as loot in Challenge Mode dungeons.
You can view your current orb inventory by pressing the golden profile crest on the top left of the town home page. Then select the "Currency" tab to see your current orbs!
Blessings of the Seeker are obtained only through the completion of the Blessings of the Seeker quest which is viewable in the Campaign tab of the quest menu. The quests start with a requirement of 100 Orbs, 250 Orbs, 500 Orbs, and then 1000 Orbs to complete, which will then repeat at 1000 orbs for each additional blessing. Each quest gives you one Blessing on the Seeker usable on any single hero.