Question:

I got a backup file with an extension .tgz - what is that and how do I open it?

Answer:

A *.tgz file is a gnu-zipped .tar file.
You can use gunzip to unpack it and afterwards tar to untar it.

You can unpack it with this command - insert your .tgz file for SAMPLE:

// 2 steps
gunzip -c SAMPLE.tgz
tar tf SAMPLE.tar

// now you should have a folder SAMPLE with your files

// or, using a pipe:
gunzip -c SAMPLE.tgz | tar tf -