The Beginning?

 I am geared up for the fight against the Wither in my most advanced world. I chose a nice, flat area in a savanna relatively far from my house, and I started constructing a wither. I left my final set of tools (aside from my bow because I have another one with Flame and Infinity) in my ender chest and brought a diamond pickaxe (Efficiency IV, Fortune III, Unbreaking III), my older sword (Sharpness IV, Fire Aspect II, Unbreaking III, Knockback II), and my final bow with Power V, Unbreaking III, Flame, and Infinity. I repaired my armor a little (the helmet was wearing out) and gathered my materials:

Ender chest
4 pieces of soul sand
3 Wither skeleton skulls
Water bucket
5 golden apples
2 potions of Strength II
5 potions of Speed II
2 potions of Regeneration II
3 splash potions of Instant Health II
Diamond Pickaxe with Efficiency IV, Fortune III and Unbreaking III
The Feral Timekeeper (Sharpness IV, Fire Aspect II, Unbreaking III, Knockback II.)
Full set of diamond armor, all at around half durability
Stack of dirt
Stack of cobblestone
19 pieces of steak
Bow with Power V, Infinity, Flame and Unbreaking III
16 arrows
2 stacks of torches (not sure why I brought them, maybe to light up the whole place if it gets dark)



During the heat of the battle, I forgot to take any screenshots. But nothing too important was missed.

I died the first two times very easily, my aiming was horrible and the boss just hovered above me and struck projectile after projectile into my face, all the while making sounds that were reminiscent of dying whales. 

I lost my full set of diamond armor, my bow, and all the stuff I had with me. I spent some days making and enchanting a full new set of armor and a new sword and some more potions. I didn't have any more apples, so I left that section alone. This time, I was lucky enough to have a Smite IV enchantment on the sword. I made another Infinity, Power V, Flame and Unbreaking III bow but left that for later. I grabbed another bow, with Power IV, took 4 stacks of arrows and headed to where I last saw the Wither.

I sniped it down to half health from an extreme hills biome when it was in a roofed forest biome. Then I drank a potion of speed II and ran towards it, striking it with my sword. Luckily, it stayed directly in front of me and I was able to kill it using the sword. 

I probably would've died if it weren't for the Blast Protection IV diamond chestplate I was wearing.

Here is a screenshot of the Nether Star, hanging above my bed in my main base.

Quite a fight, that was.