Launchd is designed to start System and Users daemon/agents located in the following places:

~/Library/LaunchAgents

- Per-user agents provided by the user

/Library/LaunchAgents

- Per-user agents provided by the administrator

/Library/LaunchDaemons

- System-wide daemons provided by the administrator

/System/Library/LaunchAgents

- Per-user agents provided by Mac OS X

/System/Library/LaunchDaemons

- System wide daemons provided by MAC OS X

How to list all launchd services:

launchctl list

Example with grepping out the apple ones:

mini:~ root# launchctl list | grep -v com.apple
PID     Status  Label
-       0       org.calendarserver.agent
25553   0       org.postfix.master.passive
-       0       org.calendarserver.archive
-       0       org.cups.cupsd
-       0       com.bresink.system.privilegedhelper-tts
-       0       org.postfix.newaliases
-       0       com.openssh.sshd
-       0       ro.gz.vms
259     0       com.vix.cron
25428   0       com.openssh.sshd
129     0       ro.gz.bs
257     0       org.ntp.ntpd
-       0       org.calendarserver.relocate

How to get details about one service:

mini:~ root# launchctl list ro.gz.bs
{
        "StandardOutPath" = "/tmp/boot-shutdown.log";
        "LimitLoadToSessionType" = "System";
        "StandardErrorPath" = "/tmp/boot-shutdown.err";
        "Label" = "ro.gz.bs";
        "TimeOut" = 30;
        "OnDemand" = true;
        "LastExitStatus" = 0;
        "PID" = 129;
        "Program" = "/etc/boot-shutdown.sh";
        "ProgramArguments" = (
                "/etc/boot-shutdown.sh";
        );
};

How to remove a launchd service:

osx$ sudo launchctl remove /Library/LaunchDaemons/com.plex.plexconnect.bash.plist

How to stop launchd services from command line:

osx$ sudo launchctl stop /Library/LaunchDaemons/com.plex.plexconnect.bash.plist

How to start launchd services from command line:

osx$ sudo launchctl start /Library/LaunchDaemons/com.plex.plexconnect.bash.plist

How to disable service at startup:

osx$ sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.softwareupdated.plist