How do I add damage to other players and not damage myself?

Player = game.Players.LocalPlayer
local Mouse = game.Players.LocalPlayer:GetMouse()
Ammo = 1
AmmoE = 1
AmmoD = 1
game:GetService("UserInputService").InputBegan:Connect(function(input)
	if input.KeyCode == Enum.KeyCode.F and Ammo>0 then
		local x = Instance.new("Part", workspace)
		x.Shape = "Ball"
		x.BrickColor = BrickColor.new("Deep orange")
		x.Transparency = 0.3
		x.TopSurface = "Smooth"
		x.BottomSurface = "Smooth"
		x.CanCollide = false
		x.Parent = workspace
		x.CFrame = Player.Character.HumanoidRootPart.CFrame*CFrame.new(0,0,-6)
		local v = Instance.new("BodyVelocity")
		v.Parent = x
		v.MaxForce = Vector3.new(math.huge, math.huge, math.huge)
		v.Velocity = (x.Position - Mouse.hit.p).unit*-100
		
		Ammo = Ammo - 1
		
		if x.Touched:Connect(function()
			if AmmoE == 1 then
				x.Transparency = 1
				local Explosion = Instance.new("Part", workspace)
				Explosion.Shape = "Ball"
				Explosion.BrickColor = BrickColor.new("Deep orange")
				Explosion.TopSurface = "Smooth"
				Explosion.BottomSurface = "Smooth"
				Explosion.CanCollide = false
				Explosion.Parent = x
				Explosion.Transparency = 0.7
				Explosion.Size = Vector3.new(20,20,20)
				Explosion.Position = x.Position
				Explosion.Anchored = true
				AmmoE = AmmoE - 1
				local StartNumber = 24
	if Explosion.Touched:Connect(function()
		if AmmoD == 1 then
			game.Players.LocalPlayer.Character.Humanoid:TakeDamage(3)
			AmmoD = AmmoD - 1
		end
	end)
	
	then end
				for i = 1,4,1 do
    			Explosion.Size = Vector3.new(StartNumber, StartNumber, StartNumber)
    			StartNumber = StartNumber + 4
    			wait(.05)
			end

			wait(0.1)
				Explosion:Destroy()
			AmmoE = 1
	end
end)
			then wait(2)
				Ammo = 1
				AmmoD = 1
		end
	end
end)

Full Code

Very vague question. However, I think you should change this part of the code to this:

if Explosion.Touched:Connect(function(plr)
    if AmmoD == 1 then
        if game.Players.LocalPlayer.Name ~= plr.Parent.Name then
            game.Workspace:FindFirstChild(plr.Parent.Name).Humanoid:TakeDamage(3)
	end
    end
    AmmoD = AmmoD - 1
end))

Hope this helps,

Tweakified