File paths are written as-
/path/to/file
Everything in your home folder is located inside /home/username/
So, if you have a file on your desktop, it is located in /home/username/Desktop/
Other partitions are mounted in /media
by default.
If you directly want to get the path of a file, you can copy the file, and paste it into your text editor, this should give you the path to your file. Put a \ before every space in the path to 'escape' the space. e.g. /media/myuseraccount/Desktop/an awesome file
would be written as:
/media/myuseraccount/Desktop/an\ awesome\ file
Another thing to note is that in Linux, your file names are case sensitive, so 'desktop' is not the same as 'Desktop'.
Finally, a shortcut to your home folder is to type ~
So, you can access your desktop by typing:
~/Desktop
and you can access your home folder by typing:
~/