Executive orders

There has been a lot of press centred around executive orders, so I thought there should be some sort of summary according to me explaining them.
I should note, abc news (that is, the Australian Broadcasting Corporation, not the local abc) does some really good summary articles too.
(see http://www.abc.net.au/news/2017-01-31/what-is-an-executive-order/8225770)

There are three branches of power - the courts, congress, and the 'executive branch' that is, the president.
Executive orders sort of bypass congress (which helps, because getting stuff through congress is sometimes sort of impossible, given the hem, politics), but they can be shown to be unconstitutional and overturned in the courts (we have a very good recent example).
They can't go against federal laws. But they can be as powerful as law. Slavery was abolished by executive order by Abraham Lincoln. And there has been a back and forth on several issues, where Republican presidents will do one thing by executive order, that Democrat presidents will then undo.
At the moment, President Trump appears to be trying to move through his list of campaign promises quickly by Executive Order. It is having mixed success, and there has been mixed reaction locally.
On one hand, he is doing what he said he would do, on the other hand, I think Congress is starting to feel left out, and to struggle with the detail required in the background of the executive orders. Repealing Obamacare would be one example, building a wall on the border with Mexico would be another.