The easiest way to tame a boar requires you to have a hunter cloak. Otherwise the boar will attack you. Crafting a hunters cloak will require a piece of meat and two animal bones. Now with the hunters cloak equipped you are ready to find a boar to tame.

Boars can be found throughout the map but there are three boars that seemingly always spawn outside Colossal Crops. These boars will give you enough materials to craft a hunters cloak and tame a boar.

It's worth mentioning there is another way to tame a boar. If you have a piece of fruit or a vegetable in your inventory, you can throw it to distract the boar while you sneak up to it and tame it.