Can't write \ character in the terminal

I was trying to do my firts course “Learn Relational Databases by Building a Mario Database” and i found myself stuck because when i press alt + <key left to key 1> nothing happens in the terminal.
I’ve tried with alt + to see what happened and nothing gets written, instead i get a message (arg: ) .
So I can’t use alt key in the terminal and that makes me not be able to do a lot of courses.

Also, after I did a bash course without problems, as i didn’t need to use any special character with alt, I entered again in the mario database course and no walkthrough messages appear.