How do I use linux command line?

Whoa! Don't use command line for installing. Use Package Manager instead which does it graphically for you automatically.

Please first check for Terminal and initiate. You will get a window which we often call as Xterminal. You wull see $ prompt or # prompt which is known as command prompt. Their you can execute commands and shell programs. Read the following books first for introduction and second for building skill in Linux/Unix

Mint is a version of Ubuntu, so I would guess it works like so. Ubuntu command line is a lot different then windows. Examples are here, but I will post a link as well. Sudo apt-get update install programname http://community.linuxmint.com/tutorial/view/244

Download the User Documentation and read about the Software Manager on Page 40

You don't have to use commandline, but I personally use it a lot. Mainly because I started on UNIX before graphic interfaces of any kind existed. But also from the commandline you have control that I don't think you ever get from a GUI (graphic user interface). There are things such as loading your pictures from a camera and you want to create thumbnails but also want them copied to a directory sized for a particular purpose. I nip onto the commandline and run my batch file for it. Takes moments to do, loads faster and more controllable than any Paint software I know of. That is just one example, I could talk about many areas where the commandline makes life easy. But, you can not jump straight into that sort of thing, you must start with one or more of the Linux tutorials. There are many free ones, start with your own Linux version tutorials.But Linux is Linux, you can read other tutorials. Debian have very good tutorials that cover nearly every Linux, because the majority are based on Devian.