So you've made your way around The High Wall of Lothric, kicked the various asses of various horrible creatures, and now you've got to take on Vordt. Don't even worry about it, we've got your back. If he gives you any trouble just read this guide and then tell him VideoGamer sent you as he bites the dust.
So we're going to assume that you already know how to open up the shortcut there, but just to refresh your memory: Vordt is past the second bonfire, and the square with the big stompy angry Winged Knight. You'll reach a big, sweeping staircase with some patrolling knights. Vordt is at the bottom and Emma the High Priestess is at the top.
When you first get into the boss fight chamber it's empty, so you have time to ember up before you go in and summon a spirit if you'd like, but it's also perfectly possible to beat him un–embered and alone. Nothing will happen until you cross over to the big overgrown doors on the other side, at which point Vordt will appear back on the opposite side of the again. He kind of looks like a big squat puppy, but on a massive, armoured scale.
Vordt's more difficult to take on if you're playing ranged. He smashes around a lot and does big long sweeps of his mace which are harder to avoid if you're keeping your middle distance, so you have to keep a large distance as you shoot whatever you're shooting at him. Just be aware that he'll charge at you, so watch for that – although he doesn't charge with that much speed until his second phase. Fire tends to be good against Vordt so if you've got any pyromancies or firebombs go with them. He takes his sweet time approaching you at the very start of the fight, so it's a good time to get some easy shots in.
For melee players the fight is actually pretty easy, especially in the first phase (touch wood). If you stand directly underneath him he basically can't hit you, so you can get right under his tummy and smash around there until he realises and charges off. Roll, rinse, repeat.
One thing for everyone to be aware of is the frost damage that stacks. As Vordt does any damage to you at all you'll see a little gauge near the bottom of the screen fill up, showing how much freezing has stacked. If it fills you're 'frostbitten' and a big chunk of your health will just disappear. If you're a bit too frosty back off and wait for it to ease off again.
Vordt's second phase is a teeny bit more troublesome, but still manageable. He starts getting a bit faster and more aggressive, with an attack that sees him charge at you three times, back and forth, in succession. This can be a pain if he hits you, but if you hold your nerve and dodge at the right time you can avoid it. Because he's a faster moving target in the second phase it can be harder for ranged attacks, so if you're tossing spells use quicker casting ones when he's moving and save the more powerful, slower casts for when he decides to sit still.
The other new attack to watch out for is when he breathes ice. When he's about to do it he'll stand still and breath in really loudly, and get a bit of an icy halo round his face, before strafing said ice breath slowly across the room. It's got a pretty fair range on it, and if it hits you then it'll do a big wallop of damage, but is, on the other hand, still easy to outrange given the size of the room. It's also a good time to get a few free hits on him, especially if you're a melee player.
If you stay calm, watch out for the frost damage, and pick your shots, then you'll be fine. We believe in you, kid.