Daily quests involve finishing number of PvP matches, skirmishes, foundry quests or finishing one of dungeons, as a reward you will get quite a lot Rough Astral Diamonds.
Such quests are available once in every 20 hours and depending on your level you will get appropriate tasks to complete. For example on level 34 you can accept daily dungeon quest requiring you to finish Lair of the Mad Dragon, and after reaching level 35 new daily quests will ask you to complete Throne of Idris.
Neverwinter allows you to collect quests from earlier levels, so you can accept Daily PvP quests whenever new are available and complete them all when you feel like it (even on level 60).
NPC Rhix in Protector's Enclave will give you new daily quests, but you can also access him from "Daily quests" module in Landing Page.