You need to experiment to find the proper size serving for the nock you are using. As for serving, do a search on the web there are a lot of tutorials online. Just remember that you need to properly serve depending on if you are left handed or right. If you serve backwards the serving will loosen over time as your fingers pull on it. I place the top loop to my left for righties, and serve from left to right, coming over the top of the string towards you. To finish pull a loop out of the serving tool and move down the string a few inches, then serve about an inch back towards yourself in the same direction, inside the loop you made. Place the serving string over the end of the serving already on the string and finish the serving by hand, unwinding the serving material as you finish, then pull the loop through, and tighten both ends..
For lefties reverse the serve, by having the serving tool going away from you over the top.