A key binding (also known as a keybind) is a method to manually bind keys to key or button-controlled actions in the game. Keybinds are very useful when it comes to switching between weapons since several of the default keys are uncomfortably far away from a player's keyboard hand.
How to Keybind
Go to the Slay.one main menu. Click on the Options gear at the top-left corner of the menu, then click the "CONTROLS" button. You should see a list of labels and buttons titled "Edit Controls". To change the key to shotgun, for example, find the "Switch to Shotgun" label and click the button next to it. The letter on the button should turn red. Then press the key you want to bind to shotgun.