how do I launch the software I downloaded?

I am new to this. I just got a imac. I downloaded Quark 5.0. When I click on launch, nothing happens. I downloaded Stuffit Lite. What do I need to do to get Quark to open up?

[MacTerminator]

Launch in LW will only work with media files (like videos and music) . With compressed applications you have to open your shared folder in the Finder and drag them onto the Stuffit Expander icon. If the .sit file unstuffs without errors (which they often don't) , a folder will be created on the desktop. Open this folder and click on the installer.