Uno to Uno "hello world" via RX/TX

I have looked at many examples on the internet to do this... all different, all I could not get to work.

I have RX on Uno "A" to the TX on Uno "B".
The Tx on "A" to Rx on "B".
The GND attached to each other.
Both Unos have their own battery.

I am still quite new to Arduino and still learning so please bare with me.

All I am looking to do is the simple "hello world" which will flash an LED if received correctly at the other Uno. This is just for learning, it is not a project... Just 2 Unos passing a string between them via Rx / Tx pins.

If anyone knows of a link with the right code for both Unos I would appreciate it very much! Thank you!

Have a look at the examples in Serial Input Basics - simple reliable ways to receive data.


Thank you