In questions of Triangles or Circles where you are required to prove something, there are cases when the help of construction is required (for example, proving the converse of Pythagoras theorem by the similarity of triangles).
My query is that
In what situation (or condition) are we supposed to use construction in geometric proofs?
[PS: I am myself in high school so my question would be more relevant to students aspiring to become mathematicians and that could be the reason my question may sound dumb]
Whenever you find yourself in this kind of situation I think you should ask yourself two questions:
Do I have/Will I find a good* proof by construction?
Does my teacher accept a proof by construction?
If you answer both questions with 'YES' you are supposed to use construction. I know that answer sounds dumb, but that is what it's all about.
*But this is important: What is good? Good for the Reader and the writer of a proof is efficiency. If you're allowed to use Theorems like Pythagoras, Congruence of triangles, Law of cosines,... take that shortcut! A proof by construction could be very long.