Player input

Keys and mouse buttons as they happen, read from a client.

Input is a client thing. The keyboard and the pointer live on that half, and the server has neither, so input code belongs in a LocalScript. UserInputService reports each key, button, and wheel turn when it happens, and answers questions about what is held right now.

React to a key

Drop a LocalScript into StarterPlayer and connect to InputBegan:

local UserInputService = game:GetService("UserInputService")

UserInputService.InputBegan:Connect(function (input)
    if input.KeyCode == Enum.KeyCode.F then
        print("flashlight")
    end
end)

Every event hands you an InputObject. KeyCode is the key for keyboard input, UserInputType separates keyboard from mouse, and Position holds the screen pixels. A wheel turn reports its amount in Position.Z.

Tell a click from a key

UserInputService.InputBegan:Connect(function (input)
    if input.UserInputType == Enum.UserInputType.MouseButton1 then
        print("clicked at", input.Position.X, input.Position.Y)
    elseif input.KeyCode == Enum.KeyCode.E then
        print("interact")
    end
end)

A click meant for an interface is better served where it lands: TextButton and the frame mouse events carry the click with no hit-testing of your own.

Ask what is held

InputBegan reports the moment a key went down. For a key that matters the whole time it is held, like sprint on Shift, ask once per frame:

local RunService = game:GetService("RunService")

RunService:BindToRenderStep("Sprint", Enum.RenderPriority.Last.Value, function ()
    if UserInputService:IsKeyDown(Enum.KeyCode.LeftShift) then
        -- sprinting this frame
    end
end)

BindToRenderStep runs before each rendered frame, on the client. Binding the same name again replaces the earlier callback, and RunService:UnbindFromRenderStep("Sprint") removes the whole thing.

The wheel arrives through InputChanged with UserInputType.MouseWheel, and GetMouseLocation() and GetMouseDelta() answer where the pointer is and how far it moved this frame.

The gameProcessed flag

Each callback also receives a gameProcessed flag. It reads false on every event: the engine's own interface does not claim input, so nothing in it takes a key away from a script.

Touch and gamepad

Neither has a path through the engine. TouchEnabled and GamepadEnabled always read false, so build for the keyboard and mouse.