Talent Points (TP) are used to upgrade skills. Every level the TP cost increases for each skill. Ultimately, a decision must be made to use one skill over another because of shortage of TP.
Ways to gain TP include doing quests. Daily quests are most geared toward TP, so it is advisable to do them if you get low on TP. TP can also be gathered by killing mobs. TP for killing mobs is calculated as 1/10 of the amount of XP recieved for killing a mob (without any buffs).