What does 上 means here?
To be above of an item = 在+ item + 上
So it means above of, on
Why 上 is in the end of the sentence, why cant it be 上桌子
Why do you include 在？
在 is used to show the location of the subject (电脑)
Does 桌子上有电脑 make any sense?
There is a computer on the table
shàngbian is a more proper way to say it I believe
May be because otherwise it would be a computer table rather than a computer on the table? (I have no clue about Chinese)
Shang position is fked up