tar -czvf aps95.tar.gz aps95/
tar -xzvf aps95.tar.gz

or

tar -cvf aps95.tar aps95/
gzip aps95.tar

gunzip aps95.tar.gz
tar -xvf aps95.tar

or

tar -cvf aps95.tar aps95/

tar -xvf aps95.tar

gunzip < file.tar.gz | tar xvf -

other

• if you don't remember what is inside the compressed archive; this command will show you the contents, again without taking apart the whole thing:

gunzip -c aps95.tar.gz | tar -tvf -

• extract bz2 files

tar xjvf cornbread.tar.bz2