mm_messages_mac displaying error questions in badi.

Hello. My question is that I don't understand what are the values that the message is taking in ?

For example:

mmpur_message_forced 'W' 'MessageID' 'MESSAGENO' text-011 '' '' ''.

I know that 'W' is like a type of error message like Warning, error, information.

But, what is 'MessageID' and 'Message No' ? How do i know which messageID or message No to use when displaying error message in PO.

Where do i go to find the error message once the message is display, is there a log ?

Thank you, I am new to displaying error messages.