If you have ever played World of Warcraft you might be familiar with the term glyph's. But if you haven't glyph's are bonus's that can help improve your skills like for example increasing how much damage a skill does. Glyphs start at around level 21 you'll receive a quest around that level from the main city telling you to go to a certain vendor to get a free one.
The glyph window is under the skills menu which can be pulled up with K if you don't see the glyph tab it is because you have not learned at least one glyph. More glyph's can be bought from the glyph vendor which is normally found standing next to your talent training in main cities only.
Later on in the game more new glyphs can be bought using badges farmed from Temple of Temerity and there are advanced versions of the glyph's which reduce the number of points required for a glyph. You can also use the NPC to reset glyph's if you don't like something you've picked although there are no dual talent spec's as of yet but its always possible it might change in the future.