OK Chun, here's how it works.
The automation page settings for trade, sal's, etc apply to new corporations you may build in the future.
If you've done your 2 weeks you can also change the automation of help on this page, including giving you the ability to set your own ed priorities. There are some extreme circumstances where your country is doing so bad that they will override you even after 2 weeks, we are told, but I've never seen this happen yet myself, could well have done though.
If you've done your 2 weeks you can set the strats of each existing corp individually or you can go to the corporations > manage page and change these things en masse.
Note the difference between the 'for new corps' and the 'existing corps'.
I hope that clears it up for you. CC