Hi @kirazen123,
welcome to the arduino-forum.
The reason why you should not use IO-pins 0,1 is:
IO-pins 0,1 are used for the hardware-serial.
If you write code that makes software-serial use the same IO-pins 0,1 as hardware-serial this is basically the same as if you call two people on two different phones and then you want to talk to both persons at the same time: doesn't work. The words will interfere and you will understand nothing.
You will have to add code to your program that realises the "transportation" of the received data from software-serial to hardware-serial to still make the data send from bluetooth visible on the serial monitor.
example:
bluetooth-receiver is connected to IO-pin 8 and 9
your code receives the data with software-serial
as pseudo-code
myBluetoothData = receiveFrom-IO-Pin 9
take data that is stored into variable myBluetoothData and send it to the serial monitor
Serial.println(myBluetoothData);
You will have to learn quite some things to understand how it really works.
You can ask as many questions as you like even hundreds of questions.
If you are willing to take advice for serious and follow the advice of experienced users your flow of questions will always be answered.
If you insist on not learning by argueing against the advice your potential helpers will turn away and answer other threads.