Destiny points are obtained when you level and can be used once you are over level 10.
For a player they are used for temporary "buffs", to include armor, will, str etc. One handy thing they can be used for is to give yourself double xp for a short time to speed up the leveling process.
You can also use them for your monster play monsters, the difference being that on your monster they are used for permament increases in stats.
Your destiny points are shared across all your toons on a server.