The Weapon Wheel is a tool you can bring up at any time to view your current equipped weaponry. At the start of the game, you have access to three slots: melee, primary, and sidearm. As you progress, you gain two more primary weapons slots. To unlock these slots, pick up the Additional Holster and Weapons Collector perks.
Having the ability to carry additional weapons is key. The more weapons you carry that have different ammo types, the more dangerous you become. Primary weapon slots can hold any type of firearm.
The sidearm slot, unsurprisingly, can hold only sidearms—pistols, small SMGs, sawed-off shotguns, and a grenade launcher.
The melee slot allows you to use either your fists or a melee weapon you’ve acquired. As you progress in the game, you’ll be able to carry additional melee weapons as well.
In addition to the weapon slots, the bottom half of the wheel contains access to all weapons as well as throwable items, such as knives, explosives, and bait.