How to see differences between files

In the case like this:

warning: /etc/bluetooth/main.conf installed as /etc/bluetooth/main.conf.pacnew

You may like to know what is the difference between these two, concisely. We use the command diff, a basic utility of Linux

An example:

diff /etc/bluetooth/main.conf /etc/bluetooth/main.conf.pacnew

Output:

264a265,269
> # This enables the GATT client functionally, so it can be disabled in system
> # which can only operate as a peripheral.
> # Defaults to 'true'.
> #Client = true
> 
311,315d315
< # This enables the GATT client functionally, so it can be disabled in system
< # which can only operate as a peripheral.
< # Defaults to 'true'.
< #Client = true
< 
362c362
< #AutoEnable=false
---
> #AutoEnable=true

> indicate what appear in the latter file and < is pointing toward the former file.