This tails the log file and the '-f' tells tail to follow the file, so anything new added to the file will also be printed to the screen.
Another option is:
less +F /var/log/messages
The +F option turns on less 'follow mode'. It is similar to tail -f but you will have the benefits of less, like scrolling up and down. To stop tailing, use Ctrl-C and to resume it, press Shift-F.
alias aptitude at awk bash bc cal cat cd colrm comm cp csh curl cut date dd df dialog diff dirname dpkg du fc find fuser grep gs gzip history iconv kill ksh last less ln ls lsof lynx m4 md5sum mkdir mkfifo mkisofs mv mysql nc netstat openssl OSX perl ping popd ps pushd python read redirection rm scp screen sed sort ssh stat sudo svn tail tar tee test top tr uniq vim wc wget xargs