You'll get a list of links to scripts in init.d beginning with either K (Kill) or S (Start). The initial letter is followed by a number which indicates the sequence in which the scripts will start. If beginning with K then the stop command will be passed to the script in init.d to which the link references. If beginning with an S then the start command will be passed.
K01dnsmasq -> ../init.d/dnsmasq
K01smartd -> ../init.d/smartd
K02avahi-daemon -> ../init.d/avahi-daemon
K02avahi-dnsconfd -> ../init.d/avahi-dnsconfd
K02NetworkManager -> ../init.d/NetworkManager
K02oddjobd -> ../init.d/oddjobd
K03yum-updatesd -> ../init.d/yum-updatesd
S00killall -> ../init.d/killall
S01halt -> ../init.d/halt
Above is a list of some of the links in a CentOS server. You'll see that dnsmasq and smartd get stopped (Kill) before avahi-daemon and so on. The scripts starting with S are there to kill remaining processes, remove lock files and some other actions before the system is halted. You can check the contents of either of the init.d script to see what they do exactly.
At this link
you can find some more basic information about runlevels and init scripts.