The terminal can be found at Applications menu -> Accessories -> Terminal.
Then type the following commands:
sudo add-apt-repository ppa:racb/extra
sudo apt-get update
sudo apt-get install pianobooster
That will build load a pre-built pianobooster binary.
To build from source is a lot more involved
You need to first how to run these commands from terminal.
https://help.ubuntu.com/community/UsingTheTerminal#File%20&%20Directory%20CommandsPlease let us know how you get on
L.