One of the greatest concepts in PoE trade currency is its own passive tree and skill gems. Every time you level up, you unlock points that you may use to uncover nodes at the passive ability tree. Minor nodes offer slight upgrades to your stats, while important nodes unlock powerful passive skills that fundamentally change how you perform.
This works in concert with skill gems, which slot into pieces of gear and give your character spells and abilities to use in combat (unlike Diablo 3, they do not have any given abilities). Items will often have numerous gem slots, and at times they are linked together. When I put an ability like Orb of Storms to a slot and then join it using Curse on Strike, Flammability and Vulnerability, each moment that my Orb of Storms hits an enemy it will also use both of these curses to them. It's basically a highly robust spell-crafting system.
Nevertheless, it's when ability gems and the tree float that things get very exciting. Obviously, I have unlocked lots of nodes which increase fire damage, but a few major nodes have these smart synergies which are really enjoyable to unlock. Take Elemental Equilibrium for example, which makes enemies I struck with elemental damage briefly get 25 percent immunity to those elements and -50 percent immunity to other components.
How can that be helpful to me? Well, when an enemy is struck by Orb of Storms, they become resistant to lightning damage but poorer to fire. And since Scorching Ray is a harm over time talent, it does not really "strike" an enemy, therefore I never risk making them more immune to buy poe chaos orbs fire by accident. That's just one of a dozen little synergies my character has. I've never been a great deal of concept crafter, but seeing my construct gradually come together since I unlock more important nodes was a rewarding experience.