1: Calling a fox can be done for different reasons — for instance, to get a seen fox closer/moved for a safe shot or to attract a fox to an area where you would like to try to shoot it.
2: The idea is to mimic the sound made by a wounded rabbit or a mouse. This should attract the fox looking for an easy meal. There are lots of ways to do this — the most common is to purse your lips and suck a “squeaky kiss” off your palm. It takes a lot of practice!
3: You can judge how your sound is being taken by the fox by its reaction. If it bolts towards you, you are on the right lines. If the fox ignores what you are doing or starts to move off, try something different or stop altogether.
4: Only shoot at a properly identified fox in a safe place with a proper back stop.
How to Squeak a fox