tar -xf filename.tar

Make sure you're in the same directory as the file. Alternatively, you could navigate to the directory the file is in using the regular graphical interface (just like you would in windows) and, I imagine, right click on the file, and do "extract," or a similar command. A tar file in Linux is basically like a zip file in windows.

EDIT: Had a few minutes, gave this a try. Apparently, tar is not sensitive to the dash, so disregard that part of what I said earlier (you can use the dash or not, both ways work). However, when you say you "got no results," you probably did. As I said, tar is basically zip. Kind of. So when you ran your tar command, it unpacked the contents of the tar file into the current directory.

Before:

KroninDirectory
filename.tar

After:

KroninDirectory
filename.tar, newFile1.txt, newFile2.rpm, newfile3.sh

At this point, you'll most likely have to run one of the files that it unpacked, if it's an automated installation of some sort.