How to make someone invinable with a click event?

script.Parent.LightButton.ClickDetector.MouseClick:Connect(function(player) -- mouseclick event is already emitted with an argument of who clicked the part
    local character = player.Character -- get the player's character
    local humanoid = character:FindFirstChild('Humanoid') -- get the character's humanoid
    if humanoid then
        humanoid.MaxHealth = math.huge -- make character invincible
        humanoid.Health = math.huge
    end
end)

QUESTION: How do I make a player invincible from clicking a button?

MouseClick has a sole parameter. This parameter passes the Player object of the player who clicked. This is how we can get the Player.

Example below. Assume YOU are the one who clicks the button.

script.Parent.LightButton.ClickDetector.MouseClick:Connect(function(playerWhoClicked)
    print(playerWhoClicked.Name) -- output: "imaginevreything"
end)

Now, in order to change a player's health, we need to access the Humanoid. Fortunately for us, we can do this via the player we just found from clicking the button. To access the Humanoid, we need to locate the Character. You can do this by running this line of code:

script.Parent.LightButton.ClickDetector.MouseClick:Connect(function(playerWhoClicked)
    local Character = playerWhoClicked.Character.Humanoid
end)

After that, we simply set the MaxHealth property to X, and Health to X aswell.

Here's the full code snippet:

script.Parent.LightButton.ClickDetector.MouseClick:Connect(function(playerWhoClicked)
    local humanoid = playerWhoClicked.Character.Humanoid
    humanoid .MaxHealth = 999999999999999999999
    humanoid .Health = 999999999999999999999
end)

Ending note: connect is deprecated, so you must use Connect.