I understand that Purpose of tightening the screws/Bolts are to fix Axial tension of the Object.
However, I need a better explanation which allow me to know about it in Depth and how to find out Bolt torque as well.
Assuming you are referring to "structural / heavy industry" applications (cf. say aerospace etc) this is one of the better publicly available resources that I have found:
Subject to the earlier assumption, you will find the torque of the fastener is generally not a criterion of consideration.
I propose although this is a good start, it is not exhaustive (and may not reflect your local requirements etc) and hence you should consult your relevant local resources etc as required.