A fairly complex constitutional issue, but for the purposes of your studies view an Executive Order as a powerful presidential tool. It carries the weight of law and does not require legislation (thus no Congresional approval is needed). It usually refers to a specific action by an agency under Executive authority. Any analysis of Presidential power should highlight this resource…
A definition could be:
executive order n. a President’s or Governor’s declaration which has the force of law, usually based on existing statutory powers, and requiring no action by the Congress or state legislature.http://legal-dictionary.thefreedictionary.com/Executive+Order
This link explains Order 9066 – the internment of the Japanese after Pearl Harbour. http://framework.latimes.com/2012/02/19/executive-order-9066-japanese-american-internment-in-world-war-ii/#/0
Some more examples:
In January 1977, following the Vietnam War, President jimmy carter directed the U.S. attorney general to cease investigating and indicting Vietnam War draft evaders (Exec. Order No. 11,967, 42 Fed. Reg. 4,393). In December 1995, President Bill Clinton ordered the U.S. reserve armed forces into active duty to augment the active armed forces’ operations in and around the former Yugoslavia (Bosnia) (Exec. Order No. 12,982, 60 Fed. Reg. 63,895).
Following the september 11th terrorist attacks on the United States, President George W. Bush used his authority to issue a number of executive orders. Following his declaration of a national emergency on September 14, 2001, he called members of the armed forces’ Ready Reserve to active duty (Exec. Order No. 13,223, 66 Fed. Reg. 48201). Ten days later, he issued an executive order that blocked the financing of terrorist organizations (Exec. Order No 13,224, 66 Fed Reg. 49079). President Bush also created the Homeland Security Department by executive order, before Congress authorized this cabinet-level department (Exec. Order No. 12,228, 66 Fed.Reg. 51812). http://legal-dictionary.thefreedictionary.com/Executive+Order