So for my new game i need to make an npc that can give this power how would i be able to do that ?
While http://robloxdev.com/articles/Shop-Dialogs
is a pretty straightforward answer by Crazycat4360, there are alternate ways to do this. There is, of course, the hard-to-do Billboard Gui
methods, and then there is game:GetService("Chat"):Chat(script.Parent, "--[[ Your text in the quotes --]]", 1 --[[1 (blue), 2 (green), or 3 (red)--]])
(http://wiki.roblox.com/index.php?title=API:Class/Chat/Chat
), and then opening a custom-made ScreenGui
for the chat feedback. Then, after the player buys said power up, you can easy give it to them.