Traits are explained on the official wiki. Once you are level 11, you can buy a manual that unlocks the ability to spend trait points. As you level, a new trait point is achieved. You will have to buy a new manual to unlock spending trait points again at level 40 and 60. There are 70 trait points available. More details and trait lines listed by profession here.
http://wiki.guildwars2.com/wiki/Trait
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