bash history expansion keywords. They select a line from the shell history and reinsert (portions of) it, possible after modification. The site you linked to does a reasonable job explaining them, but it doesn't describe all of them.
tar zxvf !#:t
doesn't actually make sense:
!# selects the line typed so far, but that's
tar zxvf and we don't want to re-use any of that. It should be
tar zxvf !$:t
which selects the last portion of the previous line (
!$), which is the URL given to
wget, and takes the filename portion (
:t, for tail — strictly speaking it's whatever's left after the last directory separator,
/, which happens to work nicely with URLs).
chown -R root:root !$:r:r
selects last portion of the previous line, drops the file extension (
:r — strictly speaking, it removes whatever's after the last
., including the
.) twice, which gives the directory name (assuming the tarball contains a directory with the same name as the tarball's base name). The
cd commands proceed in the same way.