How can I make a player to player radius gui?

So, I have tried making a hand to gui for about a month. I am an extremely better scripter now. However, it's the radius part of detecting the 3 nearest players and putting them on the list of the gui for the barista to click on. (I meant to mention this is a cafe). I am not asking for a whole enter script. That would not teach me anything. But I explained above what I do need. I can use it for future reference. At least help me out? I will give you an example of my script in the replies if you need it. Thank you!!! - Prov