How would I damage a player when they press E?

Im relatively new to scripting and this is probably a simple question but how would I damage a player when they press E on their keyboard?

@BrainDead_dev's answer is point the right the way, but the thing is, there's a feature called FilteringEnabled(FE) which makes his answer bad..

filtering enabled prevents localscripts from making changes that are visible to everyone else in the server, and this is essential to combat hackers, and exploiters.. therefore, everything that is to be replicated to all players in a game have to be done on the server.. roblox provides us with the RemoteEvents, and RemoteFunctions to do this

you can learn more about Remote Events and Remote Functions here, and on youtube - alvinblox, and also btw, since your beginner, his channel is great place to get started.. it has tutorials, and all sort of useful walkthroughs..

anyways, here's how you'd do it.

put a RemoteEvent in the ReplicatedStorage, name it\ "Damage" and do the following:

server script:

local ReplicatedStorage= game:GetService("ReplicatedStorage");

local remoteEvent = ReplicatedStorage:WaitForChild("Damage");

local damage = 20; --damage to take on a player

remoteEvent.OnServerEvent:Connect(function(player)
	local character = player.Character;

	if(not player) then return end;

	local humanoid = character.Humanoid;
	humanoid.Health = humanoid.Health - damage
end)

In a localscript:

local UserInputService = game:GetService("UserInputService")
local ReplicatedStorage= game:GetService("ReplicatedStorage");

local remoteEvent = ReplicatedStorage:WaitForChild("Damage");

UserInputService .InputBegan:Connect(function(input)
    if input.KeyCode == Enum.KeyCode.E then
	remoteEvent:FireServer()
    end
end)

Add a remote event into workspace called "Damage" Add a local script into StarterGui. in it put this code :

local UIS = game:GetService("UserInputService")

UIS.InputBegan:Connect(function(input)
	if input.KeyCode == Enum.KeyCode.E then
		local character = game.Players.LocalPlayer.Character
		workspace.Damage:FireServer(character)
	end
end)

Add a script under the remote event. Here is its code :

script.Parent.OnServerEvent:Connect(function(plr)
	local char = plr.Character
	char.Humanoid.Health = char.Humanoid.Health - 5
end)