Hello and welcome to LQ
I'd suggest you read on some basic linux commands first so that you'd know what is going on:
When you open the terminal you are in your /home/username/ directory by default. You can check it using the command:
'pwd'. Your file is on the Desktop (=/home/yourusername/Desktop)
So you need to either:
1. Change your current directory to /home/username/Desktop and untar the source there.
2. create a new directory in /home/username/ eg. 'packages', copy the source there and proceed with the installation in that directory.
To change the current directory you use 'cd'. The rest I'll leave you to research on your own:
Once you read the above info, you should be able to do stuff like that on your own. If you're stuck with
somthing, don't hesitate to ask.
PS, please use more descriptive titles in the future