(This assumes you are using tar in Linux or Cygwin.)

First, open a terminal/bash session.

Change to the root directory you want to compress, then issue this command:

tar -cvzf archive_name.tgz *

If you want to include hidden files:

tar -cvzf archive_name.tgz .

To extract the archive file, copy it to an empty directory, then issue this command:

tar -xvf archive_name.tgz