Before you start doing this, learn where they spawn as it will save you a lot of hassle in the future.

Fence or the half wall. I generally create a 2 x 2 area with 1 section missing and then wait for the boar to attack me in that area. Ignore its attack and drop the last piece in place to trap it, then jump out. Throw about 10 berries in to the pen from the safety of your workbench which you would built nearby.
Leave.
Takes a while but eventually the boar will tame and you can pet it. Sneak closer to check its progress and if its alerted, just run away,

Then you have the fun of getting it back to your camp/base/house. the easiest way is to build a series of fences to form a run and block it every so often when the boar moves along (you can push it but at some point it will try to run behind you). This can take a while so set up your run whilst the boar is taming.
Keep it simple and leave the fences once built as they can act as an extra line of defence.

When you have finally herded it where you want it (rinse and repeat until you have at least 3 of them), you can throw berries or mushrooms, or carrots (or turnips) in and they will eat and mate. Cull down to 3 now and again for lots of boar meat. As above, the 1 & 2 star boar give more meat so if you can tame them, you are golden.