Thats is what SoftwareSerial is for… check out that 2nd link I already provided
Your Arduino only has one physical serial interface (UART), and that is used for programming, or the IDE Serial Monitor, or somthing else (like hooking up a serial device), however, only one thing at a time!
So, in order to avoid conflicts, including needing to unplug your BT module every time you program the Arduino, you can instead hook the module up to those “simulated” serial ports thanks to SoftwareSerial (but keep the BAUD rate to 9600).
Only in reference to the library. Basically, just include it and thats it, as it will work for either BT or BLE.