To extract a tar file named file.tar, you can use the following command.
root@server [~]#tar -xvf file.tar
In that, the x is the part that extracts, f defines the file and v gives verbose output, telling you what is being extracted.
To extract a file that is named file.tar.gz, you will use the z flag to ungzip it as well.
root@server [~]#tar -xzvf file.tar.gz