How to make a clicker game in Roblox Studio

-- ServerScriptService > Clicker (Script)
local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local HELPERS = {
	Helper = { baseCost = 10, perSecond = 1 },
	Machine = { baseCost = 120, perSecond = 6 },
	Robot = { baseCost = 1500, perSecond = 50 },
}
local COST_GROWTH = 1.15 -- each copy costs 15% more than the last
local MAX_CLICKS_PER_SECOND = 15 -- faster clicks are ignored

local remotes = Instance.new("Folder")
remotes.Name = "ClickerRemotes"
remotes.Parent = ReplicatedStorage
local clickEvent = Instance.new("RemoteEvent")
clickEvent.Name = "Click"
clickEvent.Parent = remotes
local buyEvent = Instance.new("RemoteEvent")
buyEvent.Name = "Buy"
buyEvent.Parent = remotes

local clickWindows = {}

local function costOf(name, owned)
	return math.floor(HELPERS[name].baseCost * COST_GROWTH ^ owned)
end

local function setOwned(player, name, owned)
	player:SetAttribute(name, owned)
	player:SetAttribute(name .. "Cost", costOf(name, owned))
end

Players.PlayerAdded:Connect(function(player)
	local leaderstats = Instance.new("Folder")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player
	local clicks = Instance.new("IntValue")
	clicks.Name = "Clicks"
	clicks.Parent = leaderstats

	player:SetAttribute("PerClick", 1)
	for name in HELPERS do
		setOwned(player, name, 0) -- load saved counts here
	end
end)

Players.PlayerRemoving:Connect(function(player)
	clickWindows[player] = nil
end)

clickEvent.OnServerEvent:Connect(function(player)
	local now = os.clock()
	local window = clickWindows[player]
	if not window or now - window.start >= 1 then
		window = { start = now, count = 0 }
		clickWindows[player] = window
	end
	window.count += 1
	if window.count > MAX_CLICKS_PER_SECOND then
		return
	end
	local stats = player:FindFirstChild("leaderstats")
	if stats then
		stats.Clicks.Value += player:GetAttribute("PerClick") or 1
	end
end)

buyEvent.OnServerEvent:Connect(function(player, name)
	-- Never trust what the client sends: check the name and the price here.
	if typeof(name) ~= "string" or HELPERS[name] == nil then
		return
	end
	local stats = player:FindFirstChild("leaderstats")
	if not stats then
		return
	end
	local owned = player:GetAttribute(name) or 0
	local cost = costOf(name, owned)
	if stats.Clicks.Value < cost then
		return
	end
	stats.Clicks.Value -= cost
	setOwned(player, name, owned + 1)
end)

-- Income from helpers, once a second.
while true do
	task.wait(1)
	for _, player in Players:GetPlayers() do
		local stats = player:FindFirstChild("leaderstats")
		if stats then
			local income = 0
			for name, helper in HELPERS do
				income += (player:GetAttribute(name) or 0) * helper.perSecond
			end
			stats.Clicks.Value += income
		end
	end
end

--------------------------------------------------------------------
-- StarterGui > ClickerGui > ClickerClient (LocalScript)
local Players = game:GetService("Players")
local ReplicatedStorage = game:GetService("ReplicatedStorage")

local player = Players.LocalPlayer
local remotes = ReplicatedStorage:WaitForChild("ClickerRemotes")
local gui = script.Parent

gui:WaitForChild("ClickButton").Activated:Connect(function()
	remotes.Click:FireServer()
end)

for _, button in gui:WaitForChild("Shop"):GetChildren() do
	if button:IsA("TextButton") then
		local function refresh()
			local owned = player:GetAttribute(button.Name) or 0
			local cost = player:GetAttribute(button.Name .. "Cost") or "?"
			button.Text = button.Name .. " x" .. owned .. "  —  " .. tostring(cost)
		end
		player:GetAttributeChangedSignal(button.Name):Connect(refresh)
		player:GetAttributeChangedSignal(button.Name .. "Cost"):Connect(refresh)
		refresh()

		button.Activated:Connect(function()
			remotes.Buy:FireServer(button.Name)
		end)
	end
end