For the most part, Executive Orders are rules issued by the President that give the procedures for executive agencies to implement authorities given to the President by law or by the constitution. I worked for a career under authority of the Atomic Energy Act and Executive Order 10450, which set forth the rules for conducting background investigations for security clearances. The order was renewed and revised many times over my career. Most of the specifics of my job were spelled out by executive order, not by law.
Executive orders cannot contradict the constitution or existing law, and they can be overruled by legislation passed by Congress or by court judgments. -Joe-