Aura is a beneficial effect that gives the player a variety of bonuses depending on the Aura itself. Some of these Auras make it possible to start longer, like Patrols (up to 20 hours), others increase the amount of experience gained while levelling (Warrior), etc
Some of the Auras can be crafted in the Workshop with common resources (such as Warrior's Aura), while others can only be bought in the Royal Shop or obtained as a competition reward or as a random loot from a Lucky Chest.
There is no any limitation of using all auras same time. When aura is active it's shown below player experience bar.