I think people are mixing terminology here - depending on how forgiving people want to be one could consider "unzipping" to simply mean "extracting" which is precisely what technut explained. If the OP meant "uncompressing" then tar will do this too - just add the z parameter, ie.

to extract the files from a compressed tar file.

Note that tar on Internet Tablets is quite picky about where the z parameter appears - always put it before the f parameter otherwise tar will complain.

And to view the content of a compressed tar file, use

As a rule the filenames of compressed tar files end in .gz but this may not always be the case.