How to check if a player pressed a key?

As DetectiveRaie said, you should use :InputBegan() to simply detect user input. Also remember UIS only works in 'LocalScript' not 'ServerScript' ( RECOMMENDED ONE )

Basic Code:

local UserInputService = game:GetService("UserInputService")
local requiredKey = Enum.KeyCode.E -- key needed to run the function

UserInputService.InputBegan:Connect(function(key, gameProcessed)
	if key.KeyCode == requiredKey then
		-- Use remote event/function to comunicate with the server
        wait(10) -- cooldown
	end
end)

Next, you will need to use remote function/event since it's client sided code if you want your attacks or stuff to be seen by all players/clients ( server )

Another way of doing it by using :GetPressedKeys() ( LESS RECOMMENDED )

Your code is actually fine and correct but there is something that makes it not work.

1. You probably used ServerScript instead of LocalScript
2. In line 8 of your code there's a local function named forceField and your attacks code is inside it.
3. You forgot to call the function above
4. If you want it to be seen by the server, you must use remote event.

Before getting into the code. There' 2 ways I usually use to detect input with :GetPressedKeys(), which are UserInputService.JumpRequest and Humanoid.Running or simply just use white loop

Basic Code: ( White Loop Usage )

local UserInputService = game:GetService("UserInputService")
local requiredKey = Enum.KeyCode.R

local function getPressedKey()
	local pressedKey = UserInputService:GetKeysPressed()

	for _, key in pairs(pressedKey) do
		if key.KeyCode == requiredKey then
			print("Pressed: " , key.KeyCode)
			-- Don't forget to use remote event/function
            wait(10) -- cooldown
		end
	end
end

while wait(1) do
	getPressedKey()
end

REMINDER: ALL stuff you want to do needs to be done on the server by using remotes

FYI: You can use remote function instead of remote event to make a built in cooldown for this