How do I create fire on touch?

You can create a script inside of the part that will do this. It's pretty simple! First you want to make sure the part is actually touched by a humanoid, then you create a fire on the part. Here is the code:

local PlayersService = game:GetService("Players")

local debounce = false

script.Parent.Touched:Connect(function (hit)
	if hit and hit.Parent:FindFirstChild("Humanoid") and PlayersService:GetPlayerFromCharacter(hit.Parent) and debounce == false then
		local fire = Instance.new("Fire")
		fire.Parent = script.Parent
		debounce = true
		wait(1)
		debounce = false
	end
end)