By performing actions such as attacking, using mana, or virtually doing anything, you'll begin to learn skills associated with your actions. The skills you'll learn will make you more adept at whatever playstyle you were going for in order to obtain them in the first place. This will then cause you to use your newly gained skills to further your playstyle, and so by this process you begin to become more and more specialized in whatever field you so chose.
Every single player's skill growth is entirely unique to them, and it is encouraged to try and explore your growth and become something truly helpful and amazing.
For example, one could start out in the general field of being Offensive, then become a Swordsman, then a Dual Wielder, then (iunno) a Space Slicer...the possibilities are quite literally endless.
How to Find the Right Path for YouEdit
In general, a player will focus on either Offense or Support. From there however, the sky's the limit; you can focus on morale, or healing, or lightning, or twilight, or defense, or rainbows, or diplomacy, or anything!
Just play the game how you think is best and is satisfying, and you'll probably end up in a role equipped with skills you enjoy.