How can I find the players humanoid?

Depends if its client or server, ill show you two ways of doing it.

CLIENT

local Players = game:GetService("Players")

local Player = Players.LocalPlayer
local Character = Player.Character or Player.CharacterAdded:Wait()

local Humanoid = Character.Humanoid --add a find first child if u want to

SERVER Depends, on what ur doing, but u can do something like this

game.Players.PlayerAdded:Connect(function(Player)
	Player.CharacterAdded:Connect(function(Character)
		local Humanoid = Character.Humanoid --add a find first child if u want to
	end)
end)

Would look better if u use local functions tho, but its just an example so.