Learn the stone system and take advantage of poe currency service gems
To get new skills in Path of Exile, you'll usually have to equip stone into sockets in your gear. Any class can use any skill, but stone do have stat and level requirements. Stone can only be outfitted in slots of the same colour.
Skill gems: All these include an attack, charm, projectile, or trap/mine. Support gems: These gems modify supportable abilities when equipped in a connected socket (one with a line drawn to another socket). The support gem has to be compatible with the stone in the connected socket so as to get an effect. For instance, a service gem which affects projectiles will not do anything to some connected melee attack stone. Make sure your linked gems are compatible!
Equipped gems also level up as you make XP, getting ten percent of the foundation XP awarded from monster kills. Your personality experiences an XP penalty when revisiting lower level areas, but that punishment does not apply to gems. So you can quickly level gems by replaying areas which are a couple of levels lower than your existing degree.