how to launch an app from a qemu VM , using a command in my Linux terminal?
 

Just how?

without details hard to say more, just type the command, and press enter.

any screenshots?

you should have give the Linux distro that you are using.

assuming you have the distro up and running fine.

open terminal, and just type the name of the app.

Example: vi, vim, nano

Or Using the full path: /usr/bin/gedit