I couldn't find any clue in the Dwarf Fortress documentation about what is displayed on the left and right borders of the screen besides the number in the bottom right corner being the current level.
Can you point me to a documentation or just explain what I'm seeing there?
Best Answer
On the left side, the colored letters near the top note if there are reports that you haven't looked at. Different letters stand for different reports (source). C is combat, H is hunting, S is sparring (military).
On the right side:
The top bar shows if you are paused and the current number of idlers (dwarfs without a task to do). In older versions, the idlers will instead be on the bottom.