how to untar/tar

tar is used to create a Tape ARchive. The resulting file is known as a
tarball. It's pretty much the same concept as a ZIP file, if you know what they are,
but without the compression. To get the files out of a tarball, you can use the
following commands:

tar xvf something.tar

If the tarball has also been gzipped (compressed), you can use the following command:

tar xvfz something.tar.gz

If you only want certain directories from the tarball, do this:

tar xvzf something.tar.gz */dir.you.want/*

If you have a .tar.bz2 file, then you need bzip2 installed
(/usr/ports/archivers/bzip2), and you issue this command:

tar yxf something.tar.bz2
   

tar

To tar up *.db in the current directory into a tarball called blah.tar.gz, issue this
command:

tar cfz blah.tar.gz *.db

The z option compresses.

listing the contents

To see a list of the files within a tarball, issue the following command:

tar -tzf blah.tar.gz

The -t provides a list. the -z indicates that the tarball is compressed.

The -f identifies the tarball.

Here's an example:

# tar -tzf makeworld.991126.tgz
etc/
etc/protocols
etc/aliases
etc/services
etc/hosts

Source: http://www.freebsddiary.org/untar.php