To gain new abilities in Path of Exile, you'll usually need to equip stone into poe currency sockets on your equipment. Any class can use any skill, but stone do have stat and degree demands. Gems can only be equipped in slots of the same colour.

Skill gems: These add an attack, spell, projectile, or trap/mine. Support stones: All these gems modify supportable skills when equipped at a connected socket (one with a line drawn to some other socket). The support gem has to be compatible with the stone at the linked socket so as to have an effect. For instance, a service gem which affects projectiles won't do anything to some linked melee attack stone. Ensure that your linked jewels are compatible!

Equipped gems also level up as you earn XP, getting ten percent of the base XP awarded from monster kills. Your character encounters an XP penalty when revisiting lower level areas, but that penalty doesn't apply to stone. Thus you can quickly level gems by replaying areas that are a few degrees lower than your existing degree.

Do not pick up every single piece of loot you locate

Each piece of loot you acquire takes up varying amounts of space in your luggage compartment. To take as many possible things at the same time, you have to move things around and squeeze items into the allotted spaces. Even then, your bag is likely to fill up quickly if you pick up each and every item you encounter.

The trick, then, would be to ignore items that your character can not use or are of low price. Item rarity is indicated by poe currency buy colors: White: Norma,Blue: Magic,Yellow: Rare, Orange: Unique.