how to make when pressing "E" punch animation?

You'd first need to detect the key input, which can be done by:

local UIS = game:GetService('UserInputService')

UIS.InputBegan:Connect(function(key) --detect key input
	if key.KeyCode == Enum.KeyCode.E then --checks if the input was the E key
		-- do stuff (explained later) --
	end
end)

If the user inputted "E", we can go ahead and play an animation. Humanoid:LoadAnimation() has been deprecated, so we should instead use an Animator.

local UIS = game:GetService('UserInputService')
local Animator = Instance.new('Animator')
local Animation = Instance.new('Animation')

local Player = game:GetService('Players').LocalPlayer
local Character = Player.Character or Player.CharacterAdded:Wait() --get the player/character

Animator.Parent = Character:WaitForChild('Humanoid')
Animation.Parent = Animator
Animation.AnimationId = 'rbxassetid://animationid'

UIS.InputBegan:Connect(function(key) --detect key input
	if key.KeyCode == Enum.KeyCode.E then --checks if the input was the E key
		local Track = Animator:LoadAnimation(Animation)
		Track:Play() -- if so, load and play an animation
	end
end)

As for the damaging part, we can just detect when a body part is hit while the animation is still playing. Something like:

Character['Left Arm'].Touched:Connect(function(hit)
	if hit.Parent:FindFirstChild('Humanoid') and Track.IsPlaying then
		hit.Parent.Humanoid:TakeDamage(5)
	end
end)