when I click "download" Shutter for v12.04 in Ubuntu Softwarecenter, a window of Launch Application pops up stating: "This link needs to be opened with an application". I have no clue which application that may be. Do you?
The link you clicked will download the .deb file (the packaged version of a software) and you should open it by browsing to the
/usr/bin/ directory and then choosing
software-properties-gtk as the application to open the link.
It is easier to install shutter using the software center. Open software center by typing "software center" on the dash and then type "shutter" on the search bar and press Return and then enter your password if prompted and this will install the application for you.
You could also install shutter from the terminal. Open a terminal using Ctrl+Alt+t and then type
sudo apt-get install shutter
and enter your password if prompted and then type Return twice to install the application.