I am trying to communicate through two, Arduino UNO and Nano. Looks like it is communicating not showing any error code even, but data showing in serial monitor is a set of codes inclusive of some simples like "??!!!A" randomly...
Have a look at the examples in Serial Input Basics - simple reliable ways to receive data. There is also a parse example to illustrate how to extract numbers from the received text.
The technique in the 3rd example will be the most reliable.
You can send data in a compatible format with code like this