I don't understand how to access keyboard input?

use userinputservice or keydown if its for roblox(keydown is deprecated)

local mouse = game.Player.LocalPlayer:GetMouse() mouse.Keydown:Connect(function(key) --Happening end)

local db = false -- debounce since it's usually necessary
local uis = game:GetService("UserInputService") -- get userinputservice
    uis.InputBegan:connect(function(input, gp) -- when a input from any device happens
--input is the argument for the input object that was activated, gp is gameprocessed.
        if gp then -- if we're in the pause menu or chatting or something where you don't want to pick up a key press, end the function.
            return
        else
            if (input.UserInputType == Enum.UserInputType.Keyboard) and not db then -- if we're on keyboard and debounce is false.
                if (input.KeyCode == Enum.KeyCode.X) then -- if our input object was the X key.
                    db = true -- debounce is now true.
                    -- do anything
                    wait(3) -- our cooldown for the function to trigger
                    db = false -- let the function trigger once more
                end
            end
        end
    end)