I am a beginner user of Ubuntu 18.04. I want to use proxy server to my laptop.So I just try and find the way of using proxy server at the internet and follow mention at the website. I had no idea which is wrong. At terminal it ever say like this "E :Syntax error/etc/apt/apt.conf:3: Extra junk at the end of file " whatever I type . So I want to know how to fix it or how to remove it.Help me plz.