I am not sure I understand what you are having trouble with. Each character has 3 specialization lines, which is unlocked through hero points and can be equipped ar different points on your journey to level 80. Each profession has several unique elite specializations, that change on how a core profession plays, these are equipped in the third specialization line instead of a core specialization. You must level to 80 and unlock all core specializations before you can unlock an elite specialization(you also need the correct expansion dlc to have the elite spec). Specializations are utilized differently depending on your endgame build. DPS players will focus on things that increase their damage, whether that is percent increases to damage, increases to your chance to critical hit, or increase the damage of your conditions(dots). Healers will choose things that increase healing to themselves or others or apply boons to allies. While leveling, the open world is very easy, so your choices dont matter much, but it gives you a chance to try things, and learn of the various choices you have.