Armor Shop GUI/How to make it work?

so what im wondering is how do i make an armor shop for an RPG game i am fairly new to lua and know very few commands, but any of the shop models i use dont work how i want them to, i want a gui that i can just click a button and it will put armor on my guy, if he has enough gold, and is a high enough lvl

watch this video it helped me part one:-http://www.youtube.com/watch?v=mqXTRQI2OFE

part two:- http://www.youtube.com/watch?v=9jBiX78rKtI

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