How do i make a working money on NPC kill script that goes into a GUI?

I've been wanting to make a game like Hands of Death for awhile now, but the GUI and shop GUI and literally everything except the weapons are the issues. I've tried some code from a different question on here, but it didn't work, https://scriptinghelpers.org/questions/110401/does-someone-have-a-script-money-on-kill-on-npc-that-adds-the-cash-to-a-gui-not-leaderboard that is the question i got the code from but i don't know where the last part is supposed to go.

Here's the part that's giving me issues: while wait() do local leaderstats=game.Players.LocalPlayer:WaitForChild("leaderstats",60) script.Parent.Text="$".. tostring(leaderstats.Stats.Cash.Value) end

Where does that code go? "then because you want it in a gui, we make the gui and textlabel to display the cash value, since adding numbers to the text property of gui would be weird." is what it says before that. I have no experience in scripting, so... this could be incredibly simple and i just don't understand. If you don't understand what i mean i'll try to explain better.