A few things here that took some getting used to compared to other action games. At least for me. I never played Tera, but I did play a lot of dark souls so take it with a grain of salt.
Item usage and weapon, "weight." If you use the lance, gun lance, great sword, switch axe (axe mode), heavy bow gun, etc you will move considerably slower than normal if you have the weapon unsheathed. This creates a kind of awkward mechanic to get used to where you need to sheathe and unsheathe your weapon constantly for dodging (using the invincibility frame superman dive as they call it, you can't take any damage but requires you to run at full speed away from a monster and jump for it to work).
Second part about is about item usage. Unless using Sword and Shield. You need to run off sheathe your weapon then drink a potion. Healing Potions are overtime in this game so you will sit there sipping on it (you can slowly walk around while sipping) and any damage taken will interrupt the heal. But you will receive a portion of the healing for the time you sipped. This goes for using any item and they take varying times to be used (from instantaneous to several seconds). You are vulnerable while trying to use them. Learning when to do so is another level of depth to the game.
It all becomes natural quick enough though.