How do I set up ingame player points and purchasable items?

I don't really know where to start, I need help. Here's my place: [http://www.roblox.com/games/192793123/]

I want to give 5 player points per kill. I don't really think this is too complicated, but I don't really even grasp the basic concepts and key functions to how it would work. Someone please help me understand this and if possible help me build the script.

In addition I want to sell this gamepass in-game on a surface GUI: http://www.roblox.com/--item?id=225242953 I don't really understand the basic concepts *and *key functions for this either, but I do understand a bit how to set-up GUI's. Please help, Thanks!