# hello is a directory
$ ls .
hello tryouts somedir
# Compress
$ tar czvf hello.tar.gz hello
# Change to a directory to experiment
$ cd tryouts && mv ../hello.tar.gz .
# Extract
$ tar zxvf hello.tar.gz
$ ls
hello
# Cleanup
$ cd .. && rm -rf tryouts
# hello has two directories
$ ls hello
world greeting
# Compress, with change directory option
$ tar czvf hello.tar.gz -C hello .
# Change to a directory to experiment
$ cd tryouts && mv ../hello.tar.gz .
# Extract
$ tar zxvf hello.tar.gz
$ ls
hello.tar.gz world greeting
# Notice magic? No parent directory when extracting
# hello has two directories
$ ls hello
world greeting
# Compress, with change directory option and select world dir only
$ tar czvf hello.tar.gz -C hello world
# Change to a directory to experiment
$ cd tryouts && mv ../hello.tar.gz .
# Extract
$ tar zxvf hello.tar.gz
$ ls
hello.tar.gz world
# See? No greeting dir because we did not compress it