Go to http://dev.bukkit.org/server-mods/websend/pages/ for information on syntax and more.

Scripts like the minecraft.php are used in a bukkit -> php -> bukkit connection. These are triggered by either someone typing /ws or /websend. Other events (like player join, player bed enter, player bucket empty, ...) are available with the WSEvents plugin

Scripts like the supplied "ExternalTimeSet.php" can be used to send a command to the bukkit server, without needing an event from the bukkit server first.
This is useful for applications like registration forms (whitelisting), online server setting adjustment (time set), ect...
To be able to use this, activate the WEBLISTENER_ACTIVE in the plugin settings.