still after few years studying English I do not know quite a few things.
For example I just sketched something to the white-board and I refer to the sketch as
In the above system
In the system above.
How do you find which word order is correct?
This use of 'above' is only found in writing. It means 'previously-stated'.
For example, I told you in the sentence above that you can't use it for white-boards. And the previous sentence could have read. "I told you in the above sentence ..." So you get to choose (as happens with 'below', and quite a few other adjectives).
Note that it's not always physically above; it could be lower on the previous page.
You can also use 'above-mentioned'. "The above-mentioned professor will teach the next class."
It can also be used as a noun-substitute if the referent is easily understood: "I hope the above answers your question."