basically you get a kenetic weapon, a elemental weapon, and a "power weapon". kenetic weapons are weapons that do not have any elemental damage on them. IE - all the non exotic primary weapons post TTK. they are basically primary weapons from destiny 1 but with a few new additions (miniguns and SMGs to name 2 that are known) energy weapons or "elemental" weapons are weapons with a elemental burn on them. IE - pre TTK raid primaries (think old fate bringer or the adapt raid exotic weapons). These are just the same as kenetic weapons but they have the elemental damage on them. Power weapons are shotguns, snipers, swords, rocket launchers, grenade lauchers, fusion rifles, etc. these function like heavy weapons from Destiny 1 but include things that was previously in the special weapon category. to put it in destiny 1 terms, this allows you to equip a hand cannon and a scout rile while having a sniper or rocket launcher or sword for a heavy weapon. essentially since the kenetic and energy weapons are both primary weapons but one with burn damage and one without it allows you load out your character with 2 of the same weapon type, or one for close range and one of long range, or med range and long range, or w /e while still keeping a sniper or rocket or machine gun for when something really needs to die. unless someone was at the event and has played it, im not sure if ammo works the same way in destiny 2 as it did in 1 but i'd guess it does.

Any weapon that can kill in one shot is now a power weapon. Everything else is grouped together & separated into kinetic & energy (elemental) categories.

Guns are now split into two groups. "Normal" weapons and power weapons. Normal weapons include Hand Cannons, Scout Rifles, Pulse Rifles, Auto Rifles, Sidearms, and Submachine Guns. "Normal" weapons are then further split between Kinetic and Energy. Kinetic weapons are just regular old guns. Energy weapons however have element damage (Arc, Solar, Void) and tend to do more damage than kinetic weapons. Both use different ammo. You can carry one Kinetic weapon and one Energy weapon. Thus you can carry two "primary" guns at the same time. Such as a Scout Rifle and a Auto Rifle. Or a Handcannon and a Submachine Gun. Or two sidearms just to screw with people. Then there are power weapons. Which include Rocket Launchers, Grenade Launchers, Sniper Rifles, Fusion Rifles, Shotguns, and Swords. Power weapons are like "heavies" in the sense they are your big high damage weapon, however they are not quite as powerful as D1 heavies and thus get ammo more frequently.

They're reordering some weapons into the heavy, now called power, slot. And they've replaced the special slot with an energy slot. The first slot is now called kinetic. So the first and second slots will be kinetic primaries and energy/elemental primaries and sidearms, I think. Kinetic weapons now deal more damage to health while energy weapons deal more damage to the shields of the same element type. The power slot now contains your shotguns, fusion rifles, sniper rifles, rocket launchers, and grenade launchers.