How Do I Make A Wither

As said before. 4 soul sand and 3 Wither Skeleton heads. (Talking about Survival mode): It's not easy to get Wither skulls, but when you are patient and use Looting3 killing Wither Skeletons, then you will get them sooner or later. Kiling Wither isn't also easy but possible.(i have killed about 12 Wither in Survival servers in hard mode). First tip: Mine an area as low as possible or like in dungeons etc. This prevents that Wither explodes around blocks and flies away. Second tip: Don't use your best armour and sword/bow, beacuse Wither explodes after spawning and also uses explode attacks, when you die, you will lose most of your stuff/armour etc. Third tip: Take potions with you, like healing potions etc.
Tactics: Before spawning Wither, mine a little tunnel for you for safe spotting with chest, where you can take your stuff. Up to the safe spot tunnel, mine another tunnel closer to wither, and make like one block high and 4 blocks wide window to see and attack wither with bow. From there you can kill easily Wither woithout getting killed. But remember, attacking Wither with bow, makes him put under protection of arrow attacks, then run down to other tunnel, hit him one time with your sword, then run back to upper tunnel. It's the most effective method to kill Wither in my opinion.
When you can't understand my description, i'm sorry, but it's hard to explain it in writing. But i use this method all the time and it's effective for me.