They are SUPPOSED TO BE "guidance" for the Executive Branch agencies that a law applies to, on how to carry out that law.
So for example, say Congress passes a law with funding, to carry out a paving project on certain designated interstate highways - then the E.O. would direct the Department of Transportation to work with its relevant agencies to set up requirements and impact analyses, and work with states to coordinate permits, construction contracts, etc., and develop a timeline for the work, with regular status updates provided at some interval.
Instead, he is using E.O.s to make "new law", which is illegal.
So in the above example, he may instead create an E.O. that ignores the list of localities cited in the law for the paving project, replacing them with the locations he wants, and then will redirect any leftover funding originally authorized by Congress, for some other use. 
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