Module 2 cat doubts

Hey while typing cat $1 a stdinput console gets opened whic I quit by ctrl+c what is this console meant by and what am I supposed to do by this line, I don’t understand.
" Start the expression to populate the variable with “cat $1” which is the command line filename input. Check the Usage above." although I search $1 is command line argument but it is not very much clear to me

Can you please rephrase your question and tell me in what milestone you are facing issues?

I sorted it out , thanks