tar

view contents of tarfile
tar -vtf my.tar
v: verbose
t: table of content
f: to be followed by tar-file name

concat all files in current directory
tar -vcf my.tar *
c: create

unpack tarfile
tar -vxf my.tar
x: extract 

extract file 'yuort' from tarfile
tar -vxf my.tar  yuort

add file(s) to tarfile
tar -vuf  my.tar y*
u: update
(add all files starting with 'y')

gzip

replace file my.tar with compressed file my.tar.gz
gzip -v my.tar
v: verbose

decompress and replace every gz-file in current directory
gzip -vd *
d: decompress