Need help utilizing a formula to assist in scheduling an efficient route for a driver

So I have a group of sites and their respective coordinates that need to be visited and inspected in the most time efficient manner. So basically what I am needing help with is let's say I visit Site A first. I now need a way to calculate which site would be closest and make the most sense to visit next. After the next site is seen I need to then find which site is closest to that one and so on. I know I can do this individually by calculating the distance from any of the sites to the rest, but lets say I have 20 sites and need a way to organize them in a manner so that if I start at Site A it will populate which site is closest to Site A. Then assuming that is Site C then I want to know which site is closest to Site C without including Site A since it would have been seen already. I have attached an excel spreadsheet which shows basically what I am looking for on a smaller scale. Thank you in advance for any help and/or guidance!!