Linux / UNIX command to open .gz files

Q. I have download files from the Internet. Each file has .gz extension. How do I open .gz files under Linux?

A. You need to use gzip / gunzip program. It is a software application used for file compression. It is based on the DEFLATE algorithm, which is a combination of LZ77 and Huffman coding. DEFLATE was intended as a replacement for LZW and other patent-encumbered data compression algorithms

How do I extract a gz file?

Use guzip command as follows:
$ gunzip file.gz
OR
$ gzip -d file.gz
To see new file, enter:
$ ls -l

How do I extract a tar.gz or .tgz file?

Files with extension tar.gz or .tgz are tar files compressed with gzip. On Unix system extract them with following command:
$ gunzip < file.tar.gz | tar xvf -
$ gunzip < file.tgz | tar xvf -

If you have GNU tar (Linux system) you can use the z option directly:
$ tar xvzf file.tar.gz
$ tar xvzf file.tgz

Source :  http://www.cyberciti.biz/faq/howto-compress-expand-gz-files/