How do I acess the leaderboard from a different script?

What you're doing in lines 5 through 25 are setting up "IntValue"s. If you run your place in Solo mode, you can see these appear under game.Players.Halmuni.leaderstats. That's also the simplest way for other scripts to access those values. ex:

local players = game.Players:GetPlayers()
for i = 1, #players do
	local leaderstats = players[i]:FindFirstChild("leaderstats")
	if leaderstats then
		print("Player", players[i].Name, "has", leaderstats.USD.Value,"USD")
	end
end

In chat you also asked about ModuleScripts. They are an excellent way to share information and functionality between scripts, but they don't automatically transfer data between server and client - you would have to script that yourself.

To illustrate, let's take a very simple module script; let's say it's at game.ReplicatedStorage.TestModule

local module = {}
local var = 0
function module.IncreaseValue()
	var = var + 1
end
function module.GetValue()
	return var
end
return module

Here's a sample server script:

local TestModule = require(game.ReplicatedStorage.TestModule)
TestModule.IncreaseValue()
print(TestModule.GetValue()) -- 1

Here's another server script:

local TestModule = require(game.ReplicatedStorage.TestModule)
wait() -- ensure that the first server script runs first
print(TestModule.GetValue()) -- also prints 1 because the state is shared

However, if a client script also existed that was identical to the last server script, it would print out '0' because the state (ie the variable 'var' and any other variables in the ModuleScript) is not shared between server and client.