The ideal scenario is to find a boar pen or abandoned structure, an abandoned shack is perfect. Repair it and place doors at either end, or leave a missing roof piece, so you can jump out after the boar is trapped inside. Leave some food inside, berries, red mushrooms, carrots, then approach your boar (it is extremely preferable to tame a 2 star boar, as they are strong and can kill most meadow denizens) and get it to chase you into the structure. Make sure to destroy the workbench you used to repair the structure, as a workbench will also antagonise boars. Keep your distance from the boar and it is advisable to be crouched and weaponless as a crouched weaponless state causes the least aggravation to wild animals,

Once your 2 star boar is tamed, tame another regular boar, preferably in the same enclosed area. Once tamed they will breed and the offspring of the 2 star will always be another 2 star boar.