You can try " tar -cf Directory.tar.gz Directory" substitute Directory for the name of the directory you want, but do a test first, as I dont know if that will work on directories the same as files.
Also type man tar and tar --help at command line for some very usefull information.
UPDATE: It looks like it does work the same. I just did a test by creating a few subdirectories and then creating a file with some words in it and then issued the above, deleted the original then issued tar -xvf test.tar.gz test and it worked!