How to tame a fox in Minecraft
Foxes are the one mob people ask how to tame that cannot be tamed at all. What you can do is breed two wild ones, because the baby trusts you from birth, and that takes some setup.
Why you cannot tame an adult
Feeding a wild fox does nothing except breed it. There is no taming action, no hearts, and no way to make an adult follow you. Unlike wolves and cats, trust is only ever assigned at birth.
So the method is: find two foxes, breed them, and keep the kit. The kit trusts you and will follow you and defend you, which is the closest the game offers.
Finding and moving them
Foxes spawn in taiga, giant tree taiga and snowy taiga. The snowy variant is white, the rest are orange, and the colour of a kit depends on the biome its parents were bred in rather than their own colour.
They are skittish and sprint away from players, so getting two into one place is the hard part. Foxes follow sweet berries, which is the reliable way to lead them, and they can be moved with a lead once you get close enough to attach one.
Build a small pen first with a fence and a gate. Fences are important because foxes jump surprisingly well and a wall two blocks high is not always enough.
Breeding and keeping the kit
Feed each adult a sweet berry. They enter love mode and produce a kit that trusts you from the moment it is born.
The kit will still try to follow its parents, so remove or separate the adults or it wanders off with them. Put a lead on the kit while it grows up, which takes about twenty minutes of real time.
A trusting fox does not flee from you, follows you around, and attacks things that attack you. It never becomes a pet in the sense a tamed wolf does, and it still picks up items off the ground and refuses to give them back.
What foxes are actually good for
They carry an item in their mouth and attack rabbits, chickens, cod, salmon and baby turtles, so a fox near a chicken coop or a turtle beach is a problem rather than a feature.
They can pick up and hold useful items, including totems of undying, and a fox holding a totem will use it when it would otherwise die. Handing one an emerald or a totem is the practical trick.
Mostly they are decorative. On a server, remember that every fox is an entity with pathfinding, so a pen full of them near spawn has a cost. The survival servers here often cap animals per claim for that reason, and the creative servers are the place to build the enclosure first.