The first thing you should do is open the Mint software center (whatever they are calling it these days) and search for 7zip for Linux. If it's in the repos ("software repositories") and you select to install it, Mint will just install it for you. Since it's Mint 14, it may still have the Synaptic Package manager easily accessible--that would be more efficient to search than some bloated "software center."
What you downloaded is the sources (source code). You can install from sources, but it is ever so much easier to install from the repos.
Here's Mint's Guide to Installing Software: http://helpsite.org/install-software-in-linux/