Bruce I have to admit they confuse me too.
An Executive Order (EO) is a 'written instruction', it falls short of being an actual law. A president cannot make or change a law, that's up to Congress. And it cannot 'exceed the POTUS's authority'.
An EO cannot violate an existing law. For example, a POTUS couldn't write an EO to lower the voting age to 16. That would require the passing of a law as the voting age is stipulated in the Constitution. But EOs have been used to 'reinterpret' a law. So, Scrotus could issue an EO saying that Social Media (SM) shouldn't 'fact check' (based on 'his' interpretation of an existing law) but he couldn't say that SM absolutely can't post anything that disagrees with him in any way (violation of 1st Amendment).
EOs can be overturned by votes in Congress and can also be overturned by the Courts as a result of legal challenges. And if Scrotus tries to 'throttle' SM I expect there will be multiple legal challenges.