When you enter the battlefield, you'll find a half-buried woman that will attack you with powerful magic. Damage her and she'll reveal her whole body. At close range, she'll attack you with her two venomous tails, her pincers or her spear. These are slow attacks that you can easily anticipate and evade. She's open after attacking with her tails so use this chance to damage her.
When she distances herself from you, anticipate that she's going to use a fast, homing soul spear. Wait until the projectiles arches towards you before you roll to the side to successfully evade them. Once below half of her HP, she will then burrow on the ground. Look closely at the moving dust on the ground, indicating her position and direction. You can't attack her during this move and you have to evade just in time when she unborrows under you.
When critically injured, she'll conjure five orbs over her. These orbs will fire delayed soul arrows which makes it hard to evade. Hopefully, the other arrows fire when you're still recovering from being knocked down or when you're behind cover. From hereon, she'll be more aggressive with her attacks, usually doing 2-3 hit combos with her weapons and limbs. Fight defensively and attack only after she finishes her combo to achieve victory.
The door behind the boss leads to the Doors of Pharros. For you convenience, find and activate the bonfire in the area first. It is located straight ahead, under the hole. Just kill the two enemies here to reach it safely. For now, head back to Tark and talk to him to get a Fragrant Branch of Yore. Talk to him again to learn the Warmup gesture.