How to detect for enter key being pressed?

The following code will print something when the R key is pressed.

function onKeyPress(inputObject, gameProcessedEvent)
    if inputObject.KeyCode == Enum.KeyCode.R then
        print("R was pressed")
    end
end

game:GetService("UserInputService").InputBegan:connect(onKeyPress)

Basically you'd be using the UserInputService and when InputBegan is fired it'd run OnKeyPress() and then you would check which key was clicked which in this example is 'R' using

if inputObject.KeyCode == Enum.KeyCode.R then

then you'd run your code

This example prints 'R was pressed' when the R key is clicked and prints 'Q was pressed' when the Q key is pressed.

function onKeyPress(inputObject, gameProcessedEvent)
    if inputObject.KeyCode == Enum.KeyCode.R then
        print("R was pressed")
       elseif inputObject.KeyCode == Enum.KeyCode.Q then
        print("Q was pressed")
    end
end

game:GetService("UserInputService").InputBegan:connect(onKeyPress)

Sourse http://http://wiki.roblox.com/index.php?title=Keyboard_input

The key code pages gives you codes for keys like Enter and Tab

Key Codes http://wiki.roblox.com/?title=API:Enum/KeyCode Hope this helped.

You can use the following to detect for the enter key

local UIS = game:GetService("UserInputService")
UIS.InputBegan:Connect(function(input,GPE)
    if input.KeyCode == Enum.KeyCode.Return then
        -- do the action here
    end
end

The keycode for enter is 13, it would be used like this

local Player = game.Players.LocalPlayer
local Mouse = Player:GetMouse()

Mouse.KeyDown:connect(function(Key)
    if Key == 13 then
        --Code
    end
end)

I do not recommend using KeyDown, as it has been deprecated